转载自系统技术非业余研究
http://blog.yufeng.info/archives/1239
我们在系统调优或者定位问题的时候，经常会发现多线程程序的效率很低，但是又不知道问题出在哪里，就知道上下文切换很多，但是为什么上下文切换，是谁导致切换，我们就不知道了。上下文切换可以用dstat这样的工具查看，比如：
----total-cpu-usage---- -dsk/total- -net/total- ---paging-- ---system-- |
usr sys idl wai hiq siq| read writ| recv send| in out | int csw |
9 2 87 2 0 1|7398k 31M| 0 0 | 9.8k 11k| 16k 64k |
20 4 69 3 0 4| 26M 56M| 34M 172M| 0 0 | 61k 200k |
21 5 64 6 0 3| 26M 225M| 35M 175M| 0 0 | 75k 216k |
21 5 66 4 0 4| 25M 119M| 34M 173M| 0 0 | 66k 207k |
19 4 68 5 0 3| 23M 56M| 33M 166M| 0 0 | 60k 197k |
$sudo stap -e 'global cnt; probe scheduler.cpu_on {cnt<<<1;} probe timer.s(1){printf("%d\n", @count(cnt)); delete cnt;}' |
每秒高达200k左右的的上下文切换， 谁能告诉我发生了什么? 好吧，latencytop来救助了!
它的官网：http://www.latencytop.org/
Skipping audio, slower servers, everyone knows the symptoms of latency. But to know what’s going on in the system, what’s causing the latency, how to fix it… that’s a hard question without good answers right now.
LatencyTOP is a Linux* tool for software developers (both kernel and userspace), aimed at identifying where in the system latency is happening, and what kind of operation/action is causing the latency to happen so that the code can be changed to avoid the worst latency hiccups.
它是Intel贡献的另外一个性能查看器，还有一个是powertop,都是很不错的工具.
Latencytop通过在内核上下文切换的时候，记录被切换的进程的内核栈，然后通过匹配内核栈的函数来判断是什么原因导致上下文切换，同时他把几十种容易引起切换的场景的函数都记录起来，这样在判断系统问题的时候能容易定位到问题。
latencytop分成2个部分，内核部分和应用部分。内核部分负责调用栈的收集并且通过/proc来暴露， 应用部分负责显示.
工作界面截图如下:
latencytop在2.6.256后被内核吸收成为其中一部分，只要编译的时候打开该选项就好，如何确认呢？
$ cat /proc/latency_stats |
Latency Top version : v0.1 |
看到这个就好了, 遗憾的是RHEL6竟然带了latencytop应用部分，而没有打开编译选项，让我们情何以堪呢？
在ubuntu下可以这么安装：
$ apt-get install latencytop |
$ sudo latencytop #就可以使用了 |
但是latencytop比较傻的是默认是开图像界面的，我们很不习惯，我们要文本界面, 自己动手把!
$ apt-get source latencytop |
$ diff -up Makefile.orig Makefile |
--- Makefile.orig 2011-03-29 20:10:29.025845447 +0800 |
+++ Makefile 2011-03-28 14:48:11.232318002 +0800 |
重新make下就好了, 文本界面出现了. 具体使用参看 man latencytop。
fcicq同学说：
加个 –nogui 参数就好了. 不需要重新编译.
谢谢！
好了,那么latencytop支持多少种的延迟原因呢？让latencytop.trans告诉你，我们也可以自己修改这个文件，把新的延迟原因加上去。
$ cat /usr/share/latencytop/latencytop.trans |
1 vfs_read Reading from file |
1 vfs_write Writing to file |
1 __mark_inode_dirty Marking inode dirty |
1 vfs_readdir Reading directory content |
1 vfs_unlink Unlinking file |
1 blocking_notifier_call_chain Blocking notifier |
1 lock_super Superblock lock contention |
1 vfs_create Creating a file |
1 KAS_ScheduleTimeout Binary AMD driver delay |
1 firegl_lock_device Binary AMD driver delay |
2 __bread Synchronous buffer read |
2 do_generic_mapping_read Reading file data |
2 sock_sendmsg Sending data over socket |
2 do_sys_open Opening file |
2 do_sys_poll Waiting for event (poll) |
2 core_sys_select Waiting for event (select) |
2 proc_reg_read Reading from /proc file |
2 __pollwait Waiting for event (poll) |
2 sys_fcntl FCNTL system call |
2 scsi_error_handler SCSI error handler |
2 proc_root_readdir Reading /proc directory |
2 ksoftirqd Waking ksoftirqd |
2 do_unlinkat Unlinking file |
2 __wait_on_buffer Waiting for buffer IO to complete |
2 pdflush pdflush() kernel thread |
2 kjournald kjournald() kernel thread |
2 blkdev_ioctl block device IOCTL |
2 kauditd_thread kernel audit daemon |
2 __filemap_fdatawrite_range fdatasync system call |
2 do_sync_write synchronous write |
2 kthreadd kthreadd kernel thread |
2 usb_port_resume Waking up USB device |
2 usb_autoresume_device Waking up USB device |
2 kswapd kswapd() kernel thread |
2 md_thread Raid resync kernel thread |
2 i915_wait_request Waiting for GPU command to complete |
2 request_module Loading a kernel module |
3 tty_wait_until_sent Waiting for TTY to finish sending |
3 pipe_read Reading from a pipe |
3 pipe_write Writing to a pipe |
3 pipe_wait Waiting for pipe data |
3 read_block_bitmap Reading EXT3 block bitmaps |
3 scsi_execute_req Executing raw SCSI command |
3 sys_wait4 Waiting for a process to die |
3 sr_media_change Checking for media change |
3 sr_do_ioctl SCSI cdrom ioctl |
3 sd_ioctl SCSI disk ioctl |
3 sr_cd_check Checking CDROM media present |
3 ext3_read_inode Reading EXT3 inode |
3 htree_dirblock_to_tree Reading EXT3 directory htree |
3 ext3_readdir Reading EXT3 directory |
3 ext3_bread Synchronous EXT3 read |
3 ext3_free_branches Unlinking file on EXT3 |
3 ext3_get_branch Reading EXT3 indirect blocks |
3 ext3_find_entry EXT3: Looking for file |
3 __ext3_get_inode_loc Reading EXT3 inode |
3 ext3_delete_inode EXT3 deleting inode |
3 sync_page Writing a page to disk |
3 tty_poll Waiting for TTY data |
3 tty_read Waiting for TTY input |
3 tty_write Writing data to TTY |
3 update_atime Updating inode atime |
3 page_cache_sync_readahead Pagecache sync readahead |
3 do_fork Fork() system call |
3 sys_mkdirat Creating directory |
3 lookup_create Creating file |
3 inet_sendmsg Sending TCP/IP data |
3 tcp_recvmsg Receiving TCP/IP data |
3 link_path_walk Following symlink |
3 path_walk Walking directory tree |
3 sys_getdents Reading directory content |
3 unix_stream_recvmsg Waiting for data on unix socket |
3 ext3_mkdir EXT3: Creating a directory |
3 journal_get_write_access EXT3: Waiting for journal access |
3 synchronize_rcu Waiting for RCU |
3 input_close_device Closing input device |
3 mousedev_close_device Closing mouse device |
3 mousedev_release Closing mouse device |
3 mousedev_open Opening mouse device |
3 kmsg_read Reading from dmesg |
3 sys_futex Userspace lock contention |
3 do_futex Userspace lock contention |
3 vt_waitactive vt_waitactive IOCTL |
3 acquire_console_sem Waiting for console access |
3 filp_close Closing a file |
3 sync_inode (f)syncing an inode to disk |
3 ata_exec_internal_sg Executing internal ATA command |
3 writeback_inodes Writing back inodes |
3 ext3_orphan_add EXT3 adding orphan |
3 ext3_mark_inode_dirty EXT3 marking inode dirty |
3 ext3_unlink EXT3 unlinking file |
3 ext3_create EXT3 Creating a file |
3 log_do_checkpoint EXT3 journal checkpoint |
3 generic_delete_inode Deleting an inode |
3 proc_delete_inode Removing /proc file |
3 do_truncate Truncating file |
3 sys_execve Executing a program |
3 journal_commit_transaction EXT3: committing transaction |
3 __stop_machine_run Freezing the kernel (for module load) |
3 sys_munmap unmapping memory |
3 sys_mmap mmaping memory |
3 sync_buffer Writing buffer to disk (synchronous) |
3 inotify_inode_queue_event Inotify event |
3 proc_lookup Looking up /proc file |
3 generic_make_request Creating block layer request |
3 get_request_wait Creating block layer request |
3 alloc_page_vma Allocating a VMA |
#3 __d_lookup Looking up a dentry |
3 blkdev_direct_IO Direct block device IO |
3 sys_mprotect mprotect() system call |
3 shrink_icache_memory reducing inode cache memory footprint |
3 vfs_stat_fd stat() operation |
3 cdrom_open opening cdrom device |
3 sys_epoll_wait Waiting for event (epoll) |
3 sync_sb_inodes Syncing inodes |
3 tcp_connect TCP/IP connect |
3 ata_scsi_ioctl ATA/SCSI disk ioctl |
3 do_rmdir Removing directory |
3 vfs_rmdir Removing directory |
3 sys_flock flock() on a file |
3 usbdev_open opening USB device |
3 lock_kernel Big Kernel Lock contention |
3 blk_execute_rq Submitting block IO |
3 scsi_cmd_ioctl SCSI ioctl command |
3 acpi_ec_transaction ACPI hardware access |
3 journal_get_undo_access Waiting for EXT3 journal undo operation |
3 i915_irq_wait Waiting for GPU interrupt |
3 i915_gem_throttle_ioctl Throttling GPU while waiting for commands |
5 do_page_fault Page fault |
5 handle_mm_fault Page fault |
5 filemap_fault Page fault |
5 sync_filesystems Syncing filesystem |
5 sys_nanosleep Application requested delay |
5 sys_pause Application requested delay |
5 evdev_read Reading keyboard/mouse input |
5 do_fsync fsync() on a file (type 'F' for details) |
5 __log_wait_for_space Waiting for EXT3 journal space |
延迟原因非常的详细.
本来到这里,我要介绍的要介绍了,但是且慢,由于这个东西要在2.6.26后的系统上使用,我们的线上系统大部分是RHEL 5U4, 2.6.18的, 我们如何使用呢?
这时候 systemtap 一如既往的前来救助了!
systemtap 1.4版本以后带了个latencytop.stp, 也是intel的贡献. 那我们试验下穷人家的latencytop.
它在那里呢?
Systemtap translator/driver (version 1.5 /0.137 non-git sources) |
Copyright (C) 2005-2011 Red Hat, Inc. and others |
This is free software; see the source for copying conditions. |
enabled features: AVAHI LIBRPM LIBSQLITE3 NSS BOOST_SHARED_PTR TR1_UNORDERED_MAP NLS |
$ ls -al /usr/share/doc/systemtap/examples/profiling/latencytap.stp |
-rwxr-xr-x 1 chuba users 16240 Feb 17 22:02/usr/share/doc/systemtap/examples/profiling/latencytap.stp |
$ sudo stap -t --all-modules /usr/share/doc/systemtap/examples/profiling/latencytap.stp |
ERROR: Skipped too many probes, check MAXSKIPPED or try again with stap -t for moredetails. |
WARNING: Number of errors: 0, skipped probes: 101 |
WARNING: Skipped due to global 'dequeue' lock timeout: 2 |
WARNING: Skipped due to global 'this_sleep' lock timeout: 99 |
kernel.trace("deactivate_task")!, (/usr/share/doc/systemtap/examples/profiling/latencytap.stp:47:1), hits: 254, cycles: 680min/43327avg/2248467max, from: kernel.trace("deactivate_task") |
kernel.trace("activate_task")!, (/usr/share/doc/systemtap/examples/profiling/latencytap.stp:58:1), hits: 255, cycles: 890min/502549avg/2271568max, from: kernel.trace("activate_task") |
kernel.function("finish_task_switch@kernel/sched.c:1969")?, (/usr/share/doc/systemtap/examples/profiling/latencytap.stp:78:7), hits: 509, cycles: 213min/1002207avg/5382852max, from: kernel.function("finish_task_switch") from: scheduler.cpu_on |
begin, (/usr/share/doc/systemtap/examples/profiling/latencytap.stp:123:1), hits: 1, cycles: 1802min/1802avg/1802max, from: begin |
begin, (/usr/share/doc/systemtap/examples/profiling/latencytap.stp:131:1), hits: 1, cycles: 227979min/227979avg/227979max, from: begin |
Pass 5: run failed. Try again with another '--vp 00001' option. |
出错了！ 原因是lock timeout, 原来stap的全局变量是用锁保护的，现在超时了！知道原因好办，打个patch吧！
$ diff -up translate.cxx.orig translate.cxx |
--- translate.cxx.orig 2011-03-22 21:26:52.000000000 +0800 |
+++ /translate.cxx 2011-03-29 20:31:28.000000000 +0800 |
@@ -5802,10 +5802,10 @@ translate_pass (systemtap_session& s) |
s.op->newline() << "#define MAXACTION_INTERRUPTIBLE (MAXACTION * 10)"; |
s.op->newline() << "#endif"; |
s.op->newline() << "#ifndef TRYLOCKDELAY"; |
- s.op->newline() << "#define TRYLOCKDELAY 10 /* microseconds */"; |
+ s.op->newline() << "#define TRYLOCKDELAY 50 /* microseconds */"; |
s.op->newline() << "#endif"; |
s.op->newline() << "#ifndef MAXTRYLOCK"; |
- s.op->newline() << "#define MAXTRYLOCK 100 /* 1 millisecond total */"; |
+ s.op->newline() << "#define MAXTRYLOCK 500 /* 1 millisecond total */"; |
s.op->newline() << "#endif"; |
s.op->newline() << "#ifndef MAXMAPENTRIES"; |
s.op->newline() << "#define MAXMAPENTRIES 2048"; |
$ sudo stap --all-modules /usr/share/doc/systemtap/examples/profiling/latencytap.stp |
ERROR: probe overhead exceeded threshold |
WARNING: Number of errors: 1, skipped probes: 0 |
Pass 5: run failed. Try again with another '--vp 00001' option. |
#又错了,这次原因是probe overhead exceeded threshold, 看下代码我们知道，脚本的开销太大了，超过正常的负载，通过查看代码可以用STP_NO_OVERLOAD来解除这个限制 |
$ sudo stap -DSTP_NO_OVERLOAD --all-modules -DMAXSKIPPED=1024 /usr/share/doc/systemtap/examples/profiling/latencytap.stp |
Reason Count Average(us) Maximum(us) Percent% |
Userspace lock contention 345 16409195 83258717 45% |
migration() kernel thread 1733 402701 3571412 5% |
Reading from a pipe 212 2922207 52151180 4% |
Waking ksoftirqd 16 16082822 59266312 2% |
Waiting for event (select) 99 2113310 28510974 1% |
kjournald() kernel thread 148 1313447 13983084 1% |
Application requested delay 94 1059898 10011409 0% |
Waiting for event (select) 38 2259444 29057362 0% |
Waiting for event (poll) 1 57582711 57582711 0% |
Application requested delay 3 19030709 36000553 0% |
Waiting for event (select) 39 1341880 5847683 0% |
这次看到结果了，哈哈，小高兴一把。但是在繁忙的系统上这个脚本的资源占用特别多，也是不爽的。 幸运的是这个脚本支持查看某个进程的延迟情况， 就是在 latencytap.stp 后面加个-x 参数。
这个脚本设计应该是支持进程ID, 但是结果写成了线程ID，属于bug！！！
动手改下吧：
$ diff -u latencytap.stp.orig latencytap.stp |
--- latencytap.stp.orig 2011-02-17 22:02:40.000000000 +0800 |
+++ latencytap.stp 2011-03-29 20:43:51.000000000 +0800 |
-function log_event:long (p:long) { return (!traced_pid || traced_pid == p) } |
+function log_event:long (p:long) { return (!traced_pid || traced_pid == task_pid(p)) } |
#func names from hex addresses |
function func_backtrace:string (ips:string) |
# check to see if task is in appropriate state: |
- if (log_event($p->pid) && (s & 3)) { |
+ if (log_event($p) && (s & 3)) { |
dequeue[$p] = gettimeofday_us(); |
probe kernel.trace("activate_task") !, |
kernel.function("activate_task") { |
- if (!log_event($p->pid)) next |
+ if (!log_event($p)) next |
$ sudo stap --all-modules /usr/share/doc/systemtap/examples/profiling/latencytap.stp -x $$ |
#如果发现出来的Reason是空行， 就把latencytap.stp里面的debug=0, 改成debug=1 |
这下终于爽了，旧内核用systemtap版本的，新内核用内核版本的，世界和谐！
通过对线上MySQL的诊断发现大部分时间花在mutex锁的竞争上来，我说过了，我会收拾你的，等着瞧！
玩得开心！
Related posts:
- SystemTap–Linux下的万能观测工具
- Systemtap的另类用法
- 再谈systemtap在ubuntu 10.10下的安装
- Systemtap辅助设置tcp_init_cwnd,免对操作系统打Patch
- 突破systemtap脚本对资源使用的限制
我们在系统调优或者定位问题的时候，经常会发现多线程程序的效率很低，但是又不知道问题出在哪里，就知道上下文切换很多，但是为什么上下文切换，是谁导致切换，我们就不知道了。上下文切换可以用dstat这样的工具查看，比如：
----total-cpu-usage---- -dsk/total- -net/total- ---paging-- ---system-- |
usr sys idl wai hiq siq| read writ| recv send| in out | int csw |
9 2 87 2 0 1|7398k 31M| 0 0 | 9.8k 11k| 16k 64k |
20 4 69 3 0 4| 26M 56M| 34M 172M| 0 0 | 61k 200k |
21 5 64 6 0 3| 26M 225M| 35M 175M| 0 0 | 75k 216k |
21 5 66 4 0 4| 25M 119M| 34M 173M| 0 0 | 66k 207k |
19 4 68 5 0 3| 23M 56M| 33M 166M| 0 0 | 60k 197k |
$sudo stap -e 'global cnt; probe scheduler.cpu_on {cnt<<<1;} probe timer.s(1){printf("%d\n", @count(cnt)); delete cnt;}' |
每秒高达200k左右的的上下文切换， 谁能告诉我发生了什么? 好吧，latencytop来救助了!
它的官网：http://www.latencytop.org/
Skipping audio, slower servers, everyone knows the symptoms of latency. But to know what’s going on in the system, what’s causing the latency, how to fix it… that’s a hard question without good answers right now.
LatencyTOP is a Linux* tool for software developers (both kernel and userspace), aimed at identifying where in the system latency is happening, and what kind of operation/action is causing the latency to happen so that the code can be changed to avoid the worst latency hiccups.
它是Intel贡献的另外一个性能查看器，还有一个是powertop,都是很不错的工具.
Latencytop通过在内核上下文切换的时候，记录被切换的进程的内核栈，然后通过匹配内核栈的函数来判断是什么原因导致上下文切换，同时他把几十种容易引起切换的场景的函数都记录起来，这样在判断系统问题的时候能容易定位到问题。
latencytop分成2个部分，内核部分和应用部分。内核部分负责调用栈的收集并且通过/proc来暴露， 应用部分负责显示.
工作界面截图如下:
latencytop在2.6.256后被内核吸收成为其中一部分，只要编译的时候打开该选项就好，如何确认呢？
$ cat /proc/latency_stats |
Latency Top version : v0.1 |
看到这个就好了, 遗憾的是RHEL6竟然带了latencytop应用部分，而没有打开编译选项，让我们情何以堪呢？
在ubuntu下可以这么安装：
$ apt-get install latencytop |
$ sudo latencytop #就可以使用了 |
但是latencytop比较傻的是默认是开图像界面的，我们很不习惯，我们要文本界面, 自己动手把!
$ apt-get source latencytop |
$ diff -up Makefile.orig Makefile |
--- Makefile.orig 2011-03-29 20:10:29.025845447 +0800 |
+++ Makefile 2011-03-28 14:48:11.232318002 +0800 |
重新make下就好了, 文本界面出现了. 具体使用参看 man latencytop。
fcicq同学说：
加个 –nogui 参数就好了. 不需要重新编译.
谢谢！
好了,那么latencytop支持多少种的延迟原因呢？让latencytop.trans告诉你，我们也可以自己修改这个文件，把新的延迟原因加上去。
$ cat /usr/share/latencytop/latencytop.trans |
1 vfs_read Reading from file |
1 vfs_write Writing to file |
1 __mark_inode_dirty Marking inode dirty |
1 vfs_readdir Reading directory content |
1 vfs_unlink Unlinking file |
1 blocking_notifier_call_chain Blocking notifier |
1 lock_super Superblock lock contention |
1 vfs_create Creating a file |
1 KAS_ScheduleTimeout Binary AMD driver delay |
1 firegl_lock_device Binary AMD driver delay |
2 __bread Synchronous buffer read |
2 do_generic_mapping_read Reading file data |
2 sock_sendmsg Sending data over socket |
2 do_sys_open Opening file |
2 do_sys_poll Waiting for event (poll) |
2 core_sys_select Waiting for event (select) |
2 proc_reg_read Reading from /proc file |
2 __pollwait Waiting for event (poll) |
2 sys_fcntl FCNTL system call |
2 scsi_error_handler SCSI error handler |
2 proc_root_readdir Reading /proc directory |
2 ksoftirqd Waking ksoftirqd |
2 do_unlinkat Unlinking file |
2 __wait_on_buffer Waiting for buffer IO to complete |
2 pdflush pdflush() kernel thread |
2 kjournald kjournald() kernel thread |
2 blkdev_ioctl block device IOCTL |
2 kauditd_thread kernel audit daemon |
2 __filemap_fdatawrite_range fdatasync system call |
2 do_sync_write synchronous write |
2 kthreadd kthreadd kernel thread |
2 usb_port_resume Waking up USB device |
2 usb_autoresume_device Waking up USB device |
2 kswapd kswapd() kernel thread |
2 md_thread Raid resync kernel thread |
2 i915_wait_request Waiting for GPU command to complete |
2 request_module Loading a kernel module |
3 tty_wait_until_sent Waiting for TTY to finish sending |
3 pipe_read Reading from a pipe |
3 pipe_write Writing to a pipe |
3 pipe_wait Waiting for pipe data |
3 read_block_bitmap Reading EXT3 block bitmaps |
3 scsi_execute_req Executing raw SCSI command |
3 sys_wait4 Waiting for a process to die |
3 sr_media_change Checking for media change |
3 sr_do_ioctl SCSI cdrom ioctl |
3 sd_ioctl SCSI disk ioctl |
3 sr_cd_check Checking CDROM media present |
3 ext3_read_inode Reading EXT3 inode |
3 htree_dirblock_to_tree Reading EXT3 directory htree |
3 ext3_readdir Reading EXT3 directory |
3 ext3_bread Synchronous EXT3 read |
3 ext3_free_branches Unlinking file on EXT3 |
3 ext3_get_branch Reading EXT3 indirect blocks |
3 ext3_find_entry EXT3: Looking for file |
3 __ext3_get_inode_loc Reading EXT3 inode |
3 ext3_delete_inode EXT3 deleting inode |
3 sync_page Writing a page to disk |
3 tty_poll Waiting for TTY data |
3 tty_read Waiting for TTY input |
3 tty_write Writing data to TTY |
3 update_atime Updating inode atime |
3 page_cache_sync_readahead Pagecache sync readahead |
3 do_fork Fork() system call |
3 sys_mkdirat Creating directory |
3 lookup_create Creating file |
3 inet_sendmsg Sending TCP/IP data |
3 tcp_recvmsg Receiving TCP/IP data |
3 link_path_walk Following symlink |
3 path_walk Walking directory tree |
3 sys_getdents Reading directory content |
3 unix_stream_recvmsg Waiting for data on unix socket |
3 ext3_mkdir EXT3: Creating a directory |
3 journal_get_write_access EXT3: Waiting for journal access |
3 synchronize_rcu Waiting for RCU |
3 input_close_device Closing input device |
3 mousedev_close_device Closing mouse device |
3 mousedev_release Closing mouse device |
3 mousedev_open Opening mouse device |
3 kmsg_read Reading from dmesg |
3 sys_futex Userspace lock contention |
3 do_futex Userspace lock contention |
3 vt_waitactive vt_waitactive IOCTL |
3 acquire_console_sem Waiting for console access |
3 filp_close Closing a file |
3 sync_inode (f)syncing an inode to disk |
3 ata_exec_internal_sg Executing internal ATA command |
3 writeback_inodes Writing back inodes |
3 ext3_orphan_add EXT3 adding orphan |
3 ext3_mark_inode_dirty EXT3 marking inode dirty |
3 ext3_unlink EXT3 unlinking file |
3 ext3_create EXT3 Creating a file |
3 log_do_checkpoint EXT3 journal checkpoint |
3 generic_delete_inode Deleting an inode |
3 proc_delete_inode Removing /proc file |
3 do_truncate Truncating file |
3 sys_execve Executing a program |
3 journal_commit_transaction EXT3: committing transaction |
3 __stop_machine_run Freezing the kernel (for module load) |
3 sys_munmap unmapping memory |
3 sys_mmap mmaping memory |
3 sync_buffer Writing buffer to disk (synchronous) |
3 inotify_inode_queue_event Inotify event |
3 proc_lookup Looking up /proc file |
3 generic_make_request Creating block layer request |
3 get_request_wait Creating block layer request |
3 alloc_page_vma Allocating a VMA |
#3 __d_lookup Looking up a dentry |
3 blkdev_direct_IO Direct block device IO |
3 sys_mprotect mprotect() system call |
3 shrink_icache_memory reducing inode cache memory footprint |
3 vfs_stat_fd stat() operation |
3 cdrom_open opening cdrom device |
3 sys_epoll_wait Waiting for event (epoll) |
3 sync_sb_inodes Syncing inodes |
3 tcp_connect TCP/IP connect |
3 ata_scsi_ioctl ATA/SCSI disk ioctl |
3 do_rmdir Removing directory |
3 vfs_rmdir Removing directory |
3 sys_flock flock() on a file |
3 usbdev_open opening USB device |
3 lock_kernel Big Kernel Lock contention |
3 blk_execute_rq Submitting block IO |
3 scsi_cmd_ioctl SCSI ioctl command |
3 acpi_ec_transaction ACPI hardware access |
3 journal_get_undo_access Waiting for EXT3 journal undo operation |
3 i915_irq_wait Waiting for GPU interrupt |
3 i915_gem_throttle_ioctl Throttling GPU while waiting for commands |
5 do_page_fault Page fault |
5 handle_mm_fault Page fault |
5 filemap_fault Page fault |
5 sync_filesystems Syncing filesystem |
5 sys_nanosleep Application requested delay |
5 sys_pause Application requested delay |
5 evdev_read Reading keyboard/mouse input |
5 do_fsync fsync() on a file (type 'F' for details) |
5 __log_wait_for_space Waiting for EXT3 journal space |
延迟原因非常的详细.
本来到这里,我要介绍的要介绍了,但是且慢,由于这个东西要在2.6.26后的系统上使用,我们的线上系统大部分是RHEL 5U4, 2.6.18的, 我们如何使用呢?
这时候 systemtap 一如既往的前来救助了!
systemtap 1.4版本以后带了个latencytop.stp, 也是intel的贡献. 那我们试验下穷人家的latencytop.
它在那里呢?
Systemtap translator/driver (version 1.5 /0.137 non-git sources) |
Copyright (C) 2005-2011 Red Hat, Inc. and others |
This is free software; see the source for copying conditions. |
enabled features: AVAHI LIBRPM LIBSQLITE3 NSS BOOST_SHARED_PTR TR1_UNORDERED_MAP NLS |
$ ls -al /usr/share/doc/systemtap/examples/profiling/latencytap.stp |
-rwxr-xr-x 1 chuba users 16240 Feb 17 22:02/usr/share/doc/systemtap/examples/profiling/latencytap.stp |
$ sudo stap -t --all-modules /usr/share/doc/systemtap/examples/profiling/latencytap.stp |
ERROR: Skipped too many probes, check MAXSKIPPED or try again with stap -t for moredetails. |
WARNING: Number of errors: 0, skipped probes: 101 |
WARNING: Skipped due to global 'dequeue' lock timeout: 2 |
WARNING: Skipped due to global 'this_sleep' lock timeout: 99 |
kernel.trace("deactivate_task")!, (/usr/share/doc/systemtap/examples/profiling/latencytap.stp:47:1), hits: 254, cycles: 680min/43327avg/2248467max, from: kernel.trace("deactivate_task") |
kernel.trace("activate_task")!, (/usr/share/doc/systemtap/examples/profiling/latencytap.stp:58:1), hits: 255, cycles: 890min/502549avg/2271568max, from: kernel.trace("activate_task") |
kernel.function("finish_task_switch@kernel/sched.c:1969")?, (/usr/share/doc/systemtap/examples/profiling/latencytap.stp:78:7), hits: 509, cycles: 213min/1002207avg/5382852max, from: kernel.function("finish_task_switch") from: scheduler.cpu_on |
begin, (/usr/share/doc/systemtap/examples/profiling/latencytap.stp:123:1), hits: 1, cycles: 1802min/1802avg/1802max, from: begin |
begin, (/usr/share/doc/systemtap/examples/profiling/latencytap.stp:131:1), hits: 1, cycles: 227979min/227979avg/227979max, from: begin |
Pass 5: run failed. Try again with another '--vp 00001' option. |
出错了！ 原因是lock timeout, 原来stap的全局变量是用锁保护的，现在超时了！知道原因好办，打个patch吧！
$ diff -up translate.cxx.orig translate.cxx |
--- translate.cxx.orig 2011-03-22 21:26:52.000000000 +0800 |
+++ /translate.cxx 2011-03-29 20:31:28.000000000 +0800 |
@@ -5802,10 +5802,10 @@ translate_pass (systemtap_session& s) |
s.op->newline() << "#define MAXACTION_INTERRUPTIBLE (MAXACTION * 10)"; |
s.op->newline() << "#endif"; |
s.op->newline() << "#ifndef TRYLOCKDELAY"; |
- s.op->newline() << "#define TRYLOCKDELAY 10 /* microseconds */"; |
+ s.op->newline() << "#define TRYLOCKDELAY 50 /* microseconds */"; |
s.op->newline() << "#endif"; |
s.op->newline() << "#ifndef MAXTRYLOCK"; |
- s.op->newline() << "#define MAXTRYLOCK 100 /* 1 millisecond total */"; |
+ s.op->newline() << "#define MAXTRYLOCK 500 /* 1 millisecond total */"; |
s.op->newline() << "#endif"; |
s.op->newline() << "#ifndef MAXMAPENTRIES"; |
s.op->newline() << "#define MAXMAPENTRIES 2048"; |
$ sudo stap --all-modules /usr/share/doc/systemtap/examples/profiling/latencytap.stp |
ERROR: probe overhead exceeded threshold |
WARNING: Number of errors: 1, skipped probes: 0 |
Pass 5: run failed. Try again with another '--vp 00001' option. |
#又错了,这次原因是probe overhead exceeded threshold, 看下代码我们知道，脚本的开销太大了，超过正常的负载，通过查看代码可以用STP_NO_OVERLOAD来解除这个限制 |
$ sudo stap -DSTP_NO_OVERLOAD --all-modules -DMAXSKIPPED=1024 /usr/share/doc/systemtap/examples/profiling/latencytap.stp |
Reason Count Average(us) Maximum(us) Percent% |
Userspace lock contention 345 16409195 83258717 45% |
migration() kernel thread 1733 402701 3571412 5% |
Reading from a pipe 212 2922207 52151180 4% |
Waking ksoftirqd 16 16082822 59266312 2% |
Waiting for event (select) 99 2113310 28510974 1% |
kjournald() kernel thread 148 1313447 13983084 1% |
Application requested delay 94 1059898 10011409 0% |
Waiting for event (select) 38 2259444 29057362 0% |
Waiting for event (poll) 1 57582711 57582711 0% |
Application requested delay 3 19030709 36000553 0% |
Waiting for event (select) 39 1341880 5847683 0% |
这次看到结果了，哈哈，小高兴一把。但是在繁忙的系统上这个脚本的资源占用特别多，也是不爽的。 幸运的是这个脚本支持查看某个进程的延迟情况， 就是在 latencytap.stp 后面加个-x 参数。
这个脚本设计应该是支持进程ID, 但是结果写成了线程ID，属于bug！！！
动手改下吧：
$ diff -u latencytap.stp.orig latencytap.stp |
--- latencytap.stp.orig 2011-02-17 22:02:40.000000000 +0800 |
+++ latencytap.stp 2011-03-29 20:43:51.000000000 +0800 |
-function log_event:long (p:long) { return (!traced_pid || traced_pid == p) } |
+function log_event:long (p:long) { return (!traced_pid || traced_pid == task_pid(p)) } |
#func names from hex addresses |
function func_backtrace:string (ips:string) |
# check to see if task is in appropriate state: |
- if (log_event($p->pid) && (s & 3)) { |
+ if (log_event($p) && (s & 3)) { |
dequeue[$p] = gettimeofday_us(); |
probe kernel.trace("activate_task") !, |
kernel.function("activate_task") { |
- if (!log_event($p->pid)) next |
+ if (!log_event($p)) next |
$ sudo stap --all-modules /usr/share/doc/systemtap/examples/profiling/latencytap.stp -x $$ |
#如果发现出来的Reason是空行， 就把latencytap.stp里面的debug=0, 改成debug=1 |
这下终于爽了，旧内核用systemtap版本的，新内核用内核版本的，世界和谐！
通过对线上MySQL的诊断发现大部分时间花在mutex锁的竞争上来，我说过了，我会收拾你的，等着瞧！
玩得开心！
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