一、tracers简介
在linux的kernel/trace目录下，有一些用于调试内核的工具，也就是tracers，包括：
- tracepoint，或者也叫做event trace。tracepoint需要手动在代码中增加，默认情况下功能类似于printk，就是用于打印信息。但在trace框架中，你可以通过操作/sys/kernel/debug/tracing下的对应文件来控制打印的开关、过滤(例如只打印特点值时的信息)，也可以配perf、ebpf进行使用。
- ftrace/function tracer。function tracer不需要手动添加，内核中的大部分函数都可以使用function trace，指定特定的function进行trace的方法是echo 函数名 > /sys/kernel/debug/tracing/set_ftrace_filter。可以配置current_tracer，不同的tracer会打印不同的信息，可以打印的信息有：进程、cpu号、时间戳、函数名、函数调用栈等。
- function graph tracer。和function trace一样，但是可以打印出函数的耗时，甚至是函数函数调用的其他函数的耗时。
- kprobe。可以类似设置gdb的断点一样去设置kprobe，可以设置在任意位置。
tracer在函数中的位置：
二、tracers的使用
tracepoint的使用例子
# 关闭trace功能
echo 0 > /sys/kernel/debug/tracing/tracing_on
# 清空trace的buffer内容
echo > /sys/kernel/debug/tracing/trace
# 开启block_rq_issue的trace
echo 1 > /sys/kernel/debug/tracing/events/block/block_rq_issue/enable
# 设置block_rq_issue的filter，dev==0x8000f0，也就是major=8，minor=240
echo dev==0x8000f0 > /sys/kernel/debug/tracing/events/block/block_rq_issue/filter
# 开启block_rq_complete的trace
echo 1 > /sys/kernel/debug/tracing/events/block/block_rq_complete/enable
# 设置block_rq_issue的filter，dev==0x8000f0，也就是major=8，minor=240
echo dev==0x8000f0 > /sys/kernel/debug/tracing/events/block/block_rq_complete/filter
# 开启trace功能
echo 1 > /sys/kernel/debug/tracing/tracing_on
执行如上命令，开启了block_rq_issue与block_rq_complete这两个event的trace，然后执行dd命令对硬盘sdp(8,240)进行数据写入，就会执行到这两个event：
dd if=/dev/zero of=/dev/sdp bs=1048576 count=10
然后我们cat这个文件：/sys/kernel/debug/tracing/trace
root:/# cat /sys/kernel/debug/tracing/trace
# tracer: nop
#
# entries-in-buffer/entries-written: 32/32 #P:4
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
dd-8289 [001] .... 77475.979607: block_rq_issue: 8,240 WS 688128 () 0 + 1344 [dd]
<idle>-0 [003] ..s. 77475.981651: block_rq_complete: 8,240 WS () 0 + 1344 [0]
kworker/3:1H-171 [003] .... 77475.981715: block_rq_issue: 8,240 WS 688128 () 1344 + 1344 [kworker/3:1H]
<idle>-0 [003] ..s. 77476.001032: block_rq_complete: 8,240 WS () 1344 + 1344 [0]
dd-8289 [001] .... 77476.001158: block_rq_issue: 8,240 WS 688128 () 2688 + 1344 [dd]
<idle>-0 [003] ..s. 77476.004895: block_rq_complete: 8,240 WS () 2688 + 1344 [0]
kworker/3:1H-171 [003] .... 77476.004924: block_rq_issue: 8,240 WS 688128 () 4032 + 1344 [kworker/3:1H]
<idle>-0 [003] ..s. 77476.008818: block_rq_complete: 8,240 WS () 4032 + 1344 [0]
dd-8289 [001] .... 77476.008939: block_rq_issue: 8,240 WS 688128 () 5376 + 1344 [dd]
<idle>-0 [003] ..s. 77476.013850: block_rq_complete: 8,240 WS () 5376 + 1344 [0]
kworker/3:1H-171 [003] .... 77476.013879: block_rq_issue: 8,240 WS 688128 () 6720 + 1344 [kworker/3:1H]
<idle>-0 [003] ..s. 77476.017696: block_rq_complete: 8,240 WS () 6720 + 1344 [0]
dd-8289 [001] .... 77476.017816: block_rq_issue: 8,240 WS 688128 () 8064 + 1344 [dd]
<idle>-0 [003] ..s. 77476.022776: block_rq_complete: 8,240 WS () 8064 + 1344 [0]
kworker/3:1H-171 [003] .... 77476.022804: block_rq_issue: 8,240 WS 688128 () 9408 + 1344 [kworker/3:1H]
<idle>-0 [003] ..s. 77476.026638: block_rq_complete: 8,240 WS () 9408 + 1344 [0]
dd-8289 [001] .... 77476.026755: block_rq_issue: 8,240 WS 688128 () 10752 + 1344 [dd]
<idle>-0 [003] ..s. 77476.030496: block_rq_complete: 8,240 WS () 10752 + 1344 [0]
kworker/3:1H-171 [003] .... 77476.030540: block_rq_issue: 8,240 WS 688128 () 12096 + 1344 [kworker/3:1H]
<idle>-0 [003] ..s. 77476.035533: block_rq_complete: 8,240 WS () 12096 + 1344 [0]
dd-8289 [001] .... 77476.035647: block_rq_issue: 8,240 WS 688128 () 13440 + 1344 [dd]
<idle>-0 [003] ..s. 77476.039417: block_rq_complete: 8,240 WS () 13440 + 1344 [0]
kworker/3:1H-171 [003] .... 77476.039445: block_rq_issue: 8,240 WS 688128 () 14784 + 1344 [kworker/3:1H]
<idle>-0 [003] ..s. 77476.043302: block_rq_complete: 8,240 WS () 14784 + 1344 [0]
dd-8289 [001] .... 77476.043425: block_rq_issue: 8,240 WS 688128 () 16128 + 1344 [dd]
<idle>-0 [003] ..s. 77476.048337: block_rq_complete: 8,240 WS () 16128 + 1344 [0]
kworker/3:1H-171 [003] .... 77476.048365: block_rq_issue: 8,240 WS 688128 () 17472 + 1344 [kworker/3:1H]
<idle>-0 [003] ..s. 77476.052200: block_rq_complete: 8,240 WS () 17472 + 1344 [0]
dd-8289 [001] .... 77476.052317: block_rq_issue: 8,240 WS 688128 () 18816 + 1344 [dd]
<idle>-0 [003] ..s. 77476.056061: block_rq_complete: 8,240 WS () 18816 + 1344 [0]
kworker/3:1H-171 [003] .... 77476.056143: block_rq_issue: 8,240 WS 163840 () 20160 + 320 [kworker/3:1H]
<idle>-0 [003] ..s. 77476.062364: block_rq_complete: 8,240 WS () 20160 + 320 [0]
我们跟踪的这两个event，可以在内核中去搜索trace_block_rq_issue和trace_block_rq_complete去看event是加在哪个位置的。block_rq_issue是在下发block io的请求时执行到，block_rq_complete是在io请求完成后执行到，从打印的内容中我们可以获取一些信息，例如我们可以通过计算两者的时间差得到这次block io的耗时。
function tracer的使用例子
我们还是以block io请求的下发与结束为例。
首先在内核代码中找到trace_block_rq_issue的调用位置，是blk_mq_start_request函数：
void blk_mq_start_request(struct request *rq)
{
struct request_queue *q = rq->q;
trace_block_rq_issue(q, rq);
if (test_bit(QUEUE_FLAG_STATS, &q->queue_flags)) {
rq->io_start_time_ns = ktime_get_ns();
rq->stats_sectors = blk_rq_sectors(rq);
rq->rq_flags |= RQF_STATS;
rq_qos_issue(q, rq);
}
WARN_ON_ONCE(blk_mq_rq_state(rq) != MQ_RQ_IDLE);
blk_add_timer(rq);
WRITE_ONCE(rq->state, MQ_RQ_IN_FLIGHT);
#ifdef CONFIG_BLK_DEV_INTEGRITY
if (blk_integrity_rq(rq) && req_op(rq) == REQ_OP_WRITE)
q->integrity.profile->prepare_fn(rq);
#endif
}
同样的，我们找到block_rq_complete这个event所属的函数是blk_update_request，那么我们就使用function trace去跟踪这两个函数：blk_mq_start_request和blk_update_request，我们看看怎么操作。
我们先确认一下这两个函数能否跟踪，在/sys/kernel/debug/tracing/available_filter_functions中查看是否包含这两个函数：
root:/# cat available_filter_functions | grep blk_mq_start_request
blk_mq_start_request
root:/# cat available_filter_functions | grep blk_update_request
blk_update_request
然后执行如下命令开启function trace：
# 关闭trace功能
echo 0 > /sys/kernel/debug/tracing/tracing_on
# 清空trace的buffer内容
echo > /sys/kernel/debug/tracing/trace
# 设置filter，只跟踪blk_update_request blk_mq_start_request
echo "blk_update_request blk_mq_start_request" > /sys/kernel/debug/tracing/set_ftrace_filter
# 设置使用的tracer
echo function > current_tracer
# 开启trace功能
echo 1 > /sys/kernel/debug/tracing/tracing_on
# tracer: function
#
# entries-in-buffer/entries-written: 98/98 #P:4
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
......
sh-10582 [003] .... 79174.296310: blk_mq_start_request <-scsi_queue_rq
<idle>-0 [001] ..s. 79174.297990: blk_update_request <-scsi_end_request
kworker/1:1H-166 [001] .... 79174.297996: blk_mq_start_request <-scsi_queue_rq
<idle>-0 [001] ..s. 79174.298878: blk_update_request <-scsi_end_request
dd-10585 [001] .... 79174.711883: blk_mq_start_request <-scsi_queue_rq
ksoftirqd/1-20 [001] ..s. 79174.711891: blk_update_request <-scsi_end_request
kworker/u8:1-10333 [002] .... 79174.715406: blk_mq_start_request <-scsi_queue_rq
ksoftirqd/2-26 [002] ..s. 79174.715414: blk_update_request <-scsi_end_request
dd-10585 [001] .... 79174.715473: blk_mq_start_request <-scsi_queue_rq
dd-10585 [001] .... 79174.715473: block_rq_issue: 8,240 WS 688128 () 0 + 1344 [dd]
<idle>-0 [003] ..s. 79174.717521: blk_update_request <-scsi_end_request
<idle>-0 [003] ..s. 79174.717522: block_rq_complete: 8,240 WS () 0 + 1344 [0]
kworker/3:1H-171 [003] .... 79174.717561: blk_mq_start_request <-scsi_queue_rq
kworker/3:1H-171 [003] .... 79174.717561: block_rq_issue: 8,240 WS 688128 () 1344 + 1344 [kworker/3:1H]
<idle>-0 [003] ..s. 79174.719552: blk_update_request <-scsi_end_request
<idle>-0 [003] ..s. 79174.719552: block_rq_complete: 8,240 WS () 1344 + 1344 [0]
......
dd-10585 [001] .... 79174.781004: blk_mq_start_request <-scsi_queue_rq
dd-10585 [001] .... 79174.781004: block_rq_issue: 8,240 WS 688128 () 16128 + 1344 [dd]
<idle>-0 [003] ..s. 79174.784723: blk_update_request <-scsi_end_request
<idle>-0 [003] ..s. 79174.784724: block_rq_complete: 8,240 WS () 16128 + 1344 [0]
kworker/3:1H-171 [003] .... 79174.784753: blk_mq_start_request <-scsi_queue_rq
kworker/3:1H-171 [003] .... 79174.784753: block_rq_issue: 8,240 WS 688128 () 17472 + 1344 [kworker/3:1H]
<idle>-0 [003] ..s. 79174.788583: blk_update_request <-scsi_end_request
<idle>-0 [003] ..s. 79174.788583: block_rq_complete: 8,240 WS () 17472 + 1344 [0]
......
几点说明：
- blk_mq_start_request与blk_update_request并没有设置像tracepoint的filter，所以会有一些其他设备的打印。
- 可以看到blk_mq_start_request打印后，紧跟着block_rq_issue；blk_update_request后紧跟着block_rq_complete。
我们还可以使用stack trace:
echo 1 > /sys/kernel/debug/tracing/options/func_stack_trace
同样是从/sys/kernel/debug/tracing/trace文件中，我们可以得到以下输出，打印了跟踪函数的调用栈：
sh-11830 [001] .... 80094.295001: blk_mq_start_request <-scsi_queue_rq
sh-11830 [001] .... 80094.295021: <stack trace>
=> ftrace_call
=> blk_mq_start_request
=> scsi_queue_rq
=> blk_mq_dispatch_rq_list
=> __blk_mq_do_dispatch_sched
=> __blk_mq_sched_dispatch_requests
=> blk_mq_sched_dispatch_requests
=> __blk_mq_run_hw_queue
=> __blk_mq_delay_run_hw_queue
=> blk_mq_run_hw_queue
=> blk_mq_sched_insert_requests
=> blk_mq_flush_plug_list
=> blk_flush_plug_list
=> blk_mq_submit_bio
=> submit_bio_noacct
=> submit_bio
=> mpage_readahead
=> blkdev_readahead
=> read_pages
=> page_cache_ra_unbounded
=> do_page_cache_ra
=> ondemand_readahead
=> page_cache_sync_ra
=> generic_file_buffered_read
=> generic_file_read_iter
=> blkdev_read_iter
=> new_sync_read
=> vfs_read
=> ksys_read
=> __x64_sys_read
=> do_syscall_64
=> entry_SYSCALL_64_after_hwframe
function graph tracer的使用例子
我们以blk_mq_start_request为例来看一下function graph tracer的使用。
我们先把前面测试中开启的trace关闭掉，并清空buffer数据：
echo 0 > /sys/kernel/debug/tracing/events/enable
echo > /sys/kernel/debug/tracing/set_ftrace_filter
echo 0 > /sys/kernel/debug/tracing/tracing_on
echo > /sys/kernel/debug/tracing/trace
然后开启对函数blk_mq_start_request的function graph trace：
# 使用function_graph作为tracer
echo function_graph > /sys/kernel/debug/tracing/current_tracer
# 设置跟踪的函数为blk_mq_start_request
echo blk_mq_start_request > /sys/kernel/debug/tracing/set_graph_function
# 设置max_graph_depth为0，不限制跟踪的深度
echo 0 > /sys/kernel/debug/tracing/max_graph_depth
# 重新开启trace
echo 1 > /sys/kernel/debug/tracing/tracing_on
再看输出：
# tracer: function_graph
#
# CPU DURATION FUNCTION CALLS
# | | | | | | |
3) 1.075 us | finish_task_switch();
1) | blk_mq_start_request() {
1) 0.207 us | ktime_get();
1) | __rq_qos_issue() {
1) 0.163 us | wbt_issue();
1) 0.458 us | }
1) | blk_add_timer() {
1) | mod_timer() {
1) | lock_timer_base() {
1) 0.095 us | _raw_spin_lock_irqsave();
1) 0.267 us | }
1) 0.081 us | detach_if_pending();
1) 0.082 us | get_nohz_timer_target();
1) 0.082 us | _raw_spin_lock();
1) | internal_add_timer() {
1) 0.091 us | calc_wheel_index();
1) 0.195 us | enqueue_timer();
1) 0.548 us | }
1) 0.085 us | _raw_spin_unlock_irqrestore();
1) 1.809 us | }
1) 2.160 us | }
1) 4.340 us | }
1) | blk_mq_start_request() {
1) 0.138 us | ktime_get();
1) | __rq_qos_issue() {
1) 0.131 us | wbt_issue();
1) 0.347 us | }
1) 0.245 us | blk_add_timer();
1) 1.978 us | }
------------------------------------------
1) sh-426 => kworker-166
------------------------------------------
1) 0.193 us | finish_task_switch();
1) | blk_mq_start_request() {
1) 0.125 us | ktime_get();
1) | __rq_qos_issue() {
1) 0.088 us | wbt_issue();
1) 0.279 us | }
1) 0.084 us | blk_add_timer();
1) 0.859 us | }
------------------------------------------
1) kworker-166 => sh-434
------------------------------------------
可以看到，blk_mq_start_request这个函数的总耗时在函数的结束位置’}’处打印出来了，其调用的各个函数的耗时也都被打印出来了，非常详细。
我们再看看设置max_graph_depth后有什么区别：
echo 1 > /sys/kernel/debug/tracing/max_graph_depth
输出变成：
1) 0.392 us | blk_mq_start_request();
------------------------------------------
3) sh-636 => sh-691
------------------------------------------
3) 2.409 us | blk_mq_start_request();
3) 1.258 us | blk_mq_start_request();
1) 0.982 us | blk_mq_start_request();
只打印了blk_mq_start_request的耗时。
kprobe的使用例子
kprobe有两种：
- 第一种是传统的使用int3断点指令来实现的，可以加在代码的任意位置。使用这种方式一般需要编写内核module，进行需要的probe的注册，将module加载之后才能插入kprobe。
- 第二种是基于ftrace做的，不需要编写module，与其他tracer一样直接操作/sys/kernel/debug/tracing/下的文件就可以控制kprobe的开关，但是应该无法指定在任意位置插入kprobe，只能在函数开头/结尾处。
由于第一种方法使用比较麻烦，本文就只介绍第二种的用法了。
还是以blk_mq_start_request函数为例：
# 插入对blk_mq_start_request函数的kprobe
echo 'p:my_test blk_mq_start_request' > /sys/kernel/debug/tracing/kprobe_events
# 插入kprobe后，会作为一个event在 /sys/kernel/debug/tracing/events/kprobe/下创建my_test目录。
# my_test这个名字是在echo到/sys/kernel/debug/tracing/kprobe_events文件中时指定的。
echo 1 > /sys/kernel/debug/tracing/events/kprobes/my_test/enable
会输出以下打印：
# tracer: nop
#
# entries-in-buffer/entries-written: 13/13 #P:4
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
sh-6034 [000] .... 3294.372995: my_test: (blk_mq_start_request+0x0/0x100)
sh-6034 [000] .... 3294.373357: my_test: (blk_mq_start_request+0x0/0x100)
kworker/1:1H-171 [001] .... 3294.375052: my_test: (blk_mq_start_request+0x0/0x100)
sh-6040 [002] .... 3299.374970: my_test: (blk_mq_start_request+0x0/0x100)
sh-6040 [002] .... 3299.375407: my_test: (blk_mq_start_request+0x0/0x100)
kworker/1:1H-171 [001] .... 3299.377144: my_test: (blk_mq_start_request+0x0/0x100)
dd-6047 [001] .... 3303.510966: my_test: (blk_mq_start_request+0x0/0x100)
kworker/u8:7-147 [002] .... 3303.511809: my_test: (blk_mq_start_request+0x0/0x100)
dd-6047 [001] .... 3303.511844: my_test: (blk_mq_start_request+0x0/0x100)
kworker/3:1H-416 [003] .... 3303.514001: my_test: (blk_mq_start_request+0x0/0x100)
我们还可以修改echo到kprobe_events的内容，来打印更多的信息，例如：
# 要修改kprobe_events，要先关闭已开启的kprobe_events
echo 0 > /sys/kernel/debug/tracing/events/kprobes/my_test/enable
# 清空之前的缓存数据
echo > /sys/kernel/debug/tracing/trace
# 打印了以下内容：
# 1.[request=$arg1]
# blk_mq_start_request函数的第一个参数，也就是struct request *rq
# 2.[+40($arg1):u32]
# 第一个参数，也就是struct request *rq，再+40后作为u32*，再取值，也就是rq->__data_len
# 3.[+48($arg1):u64]
# rq->__sector
echo 'p:my_test blk_mq_start_request request=$arg1 +40($arg1):u32 +48($arg1):u64' > /sys/kernel/debug/tracing/kprobe_events
echo 1 > /sys/kernel/debug/tracing/events/kprobes/my_test/enable
我们同时开启了block_rq_issue这个event的输出，进行对比验证：
# tracer: nop
#
# entries-in-buffer/entries-written: 20/20 #P:4
#
# _-----=> irqs-off
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / delay
# TASK-PID CPU# |||| TIMESTAMP FUNCTION
# | | | |||| | |
sh-11183 [000] .... 7129.373391: my_test: (blk_mq_start_request+0x0/0x100) request=0xffff8fd742883c00 arg2=16384 arg3=2048
sh-11183 [000] .... 7129.373392: block_rq_issue: 70,64 RA 16384 () 2048 + 32 [sh]
sh-11183 [000] .... 7129.373848: my_test: (blk_mq_start_request+0x0/0x100) request=0xffff8fd742883f00 arg2=819200 arg3=77824
sh-11183 [000] .... 7129.373850: block_rq_issue: 70,64 RA 819200 () 77824 + 1600 [sh]
kworker/1:1H-171 [001] .... 7129.375853: my_test: (blk_mq_start_request+0x0/0x100) request=0xffff8fd742884200 arg2=229376 arg3=79424
kworker/1:1H-171 [001] .... 7129.375855: block_rq_issue: 70,64 RA 229376 () 79424 + 448 [kworker/1:1H]
dd-11189 [001] .... 7132.463146: my_test: (blk_mq_start_request+0x0/0x100) request=0xffff8fd742a39300 arg2=0 arg3=18446744073709551615
dd-11189 [001] .... 7132.463148: block_rq_issue: 0,0 N 0 () 0 + 0 [dd]
......
我们找一个对比验证一下，my_test的输出：
request=0xffff8fd742883c00 arg2=16384 arg3=2048
block_rq_issue的输出：
70,64 RA 16384 () 2048 + 32 [sh]
长度16384是相等的，sector是2048页式一样的。
echo到kprobe_events的格式在trace_kprobe_create函数中的注释中有说明：
static int trace_kprobe_create(int argc, const char *argv[])
{
/*
* Argument syntax:
* - Add kprobe:
* p[:[GRP/]EVENT] [MOD:]KSYM[+OFFS]|KADDR [FETCHARGS]
* - Add kretprobe:
* r[MAXACTIVE][:[GRP/]EVENT] [MOD:]KSYM[+0] [FETCHARGS]
* Or
* p:[GRP/]EVENT] [MOD:]KSYM[+0]%return [FETCHARGS]
*
* Fetch args:
* $retval : fetch return value
* $stack : fetch stack address
* $stackN : fetch Nth of stack (N:0-)
* $comm : fetch current task comm
* @ADDR : fetch memory at ADDR (ADDR should be in kernel)
* @SYM[+|-offs] : fetch memory at SYM +|- offs (SYM is a data symbol)
* %REG : fetch register REG
* Dereferencing memory fetch:
* +|-offs(ARG) : fetch memory at ARG +|- offs address.
* Alias name of args:
* NAME=FETCHARG : set NAME as alias of FETCHARG.
* Type of args:
* FETCHARG:TYPE : use TYPE instead of unsigned long.
*/
另外，我们设置要插入kprobe的位置，是由参数[MOD:]KSYM[+OFFS]指定的，我们上面的例子就是blk_mq_start_request，也就是只有KSYM。我们传入的参数最前面是p，也可以是r，如果是p就是函数开头，r就是函数的结束位置，这两个位置是明确的，比较常用。如果有需要指定其他位置的需求，也可以加上[+OFFS]，但要能够对这个通过OFFS指定的代码位置比较了解。
三、tracer的外围工具
上面的使用例子，我们只是用了/sys/kernel/debug/tracing，也就是tracefs下的文件，进行简单的echo、cat进行分析，还有一些其他工具可以利用tracer提供的信息做更高级的分析。
trace-cmd
trace-cmd支持的命令：
trace-cmd version 2.6.1
usage:
trace-cmd [COMMAND] ...
commands:
record - record a trace into a trace.dat file
start - start tracing without recording into a file
extract - extract a trace from the kernel
stop - stop the kernel from recording trace data
restart - restart the kernel trace data recording
show - show the contents of the kernel tracing buffer
reset - disable all kernel tracing and clear the trace buffers
report - read out the trace stored in a trace.dat file
stream - Start tracing and read the output directly
profile - Start profiling and read the output directly
hist - show a historgram of the trace.dat information
stat - show the status of the running tracing (ftrace) system
split - parse a trace.dat file into smaller file(s)
options - list the plugin options available for trace-cmd report
listen - listen on a network socket for trace clients
list - list the available events, plugins or options
restore - restore a crashed record
snapshot - take snapshot of running trace
stack - output, enable or disable kernel stack tracing
check-events - parse trace event formats
以下是一些使用过程：
# 使用record命令可以记录数据，通过trace-cmd record -h可以查看可用的参数。
root:/# trace-cmd record -e block_rq_issue
Hit Ctrl^C to stop recording
^CCPU0 data recorded at offset=0x67f000 #^C结束record
4096 bytes in size
CPU1 data recorded at offset=0x680000
4096 bytes in size
CPU2 data recorded at offset=0x681000
4096 bytes in size
CPU3 data recorded at offset=0x682000
4096 bytes in size
# 生成一个trace.dat文件，应该保存的是二进制数据
root:/#ls -al
-rw-r--r-- 1 root root 6828032 Mar 25 17:04 trace.dat
# 打印trace.dat中的内容
root:/# trace-cmd report trace.dat
cpus=4
jbd2/sdcw7-8-223 [003] 9726.635682: block_rq_issue: 70,64 WS 24576 () 59795464 + 48 [jbd2/sdcw7-8]
kworker/3:1H-416 [003] 9726.635775: block_rq_issue: 70,64 FF 0 () 0 + 0 [kworker/3:1H]
kworker/1:1H-171 [001] 9726.636249: block_rq_issue: 70,64 WS 4096 () 59795512 + 8 [kworker/1:1H]
kworker/1:1H-171 [001] 9726.636280: block_rq_issue: 70,64 FF 0 () 0 + 0 [kworker/1:1H]
。。。。。。
# 对trace.dat文件进行统计分析
root:/# trace-cmd hist
CPU 0 is empty
CPU 2 is empty
%42.86 (171) kworker/1:1H block_rq_issue #3
|
--- *block_rq_issue*
%28.57 (15050) sh block_rq_issue #2
|
--- *block_rq_issue*
%14.29 (416) kworker/3:1H block_rq_issue #1
|
--- *block_rq_issue*
%14.29 (223) jbd2/sdcw7-8 block_rq_issue #1
|
--- *block_rq_issue*
perf
perf有很多功能，对tracer的信息进行记录、分析是其中一个功能。
使用例子：
# 对event block:block_rq_issue的数据进行记录，保存到perf.data
root:/# perf record -e block:block_rq_issue
^C[ perf record: Woken up 0 times to write data ] #ctrl+c停止
[ perf record: Captured and wrote 7.741 MB perf.data (62359 samples) ]
# 生成perf.data文件，是二进制数据
root:/# ls -al
-rw------- 1 root root 8128875 Mar 25 17:18 perf.data
# 使用文本形式输出
root:/# perf script > ./perf.data.script
root:/# head ./perf.data.script
perf 15915 [003] 10610.606557: block:block_rq_issue: 70,64 WS 8192 () 3892640 + 16 [perf]
jbd2/sdcw7-8 223 [001] 10610.606611: block:block_rq_issue: 70,64 WS 16384 () 59921240 + 32 [jbd2/sdcw7-8]
kworker/1:1H-kb 171 [001] 10610.606678: block:block_rq_issue: 70,64 FF 0 () 0 + 0 [kworker/1:1H]
kworker/1:1H-kb 171 [001] 10610.607076: block:block_rq_issue: 70,64 WS 4096 () 59921272 + 8 [kworker/1:1H]
kworker/1:1H-kb 171 [001] 10610.607112: block:block_rq_issue: 70,64 FF 0 () 0 + 0 [kworker/1:1H]
perf 15915 [003] 10610.607488: block:block_rq_issue: 70,64 WS 4096 () 3892648 + 8 [perf]
jbd2/sdcw7-8 223 [001] 10610.607560: block:block_rq_issue: 70,64 WS 8192 () 59921280 + 16 [jbd2/sdcw7-8]
kworker/1:1H-kb 171 [001] 10610.607605: block:block_rq_issue: 70,64 FF 0 () 0 + 0 [kworker/1:1H]
kworker/1:1H-kb 171 [001] 10610.607917: block:block_rq_issue: 70,64 WS 4096 () 59921296 + 8 [kworker/1:1H]
kworker/1:1H-kb 171 [001] 10610.607955: block:block_rq_issue: 70,64 FF 0 () 0 + 0 [kworker/1:1H]
# 进行统计分析
root:/# perf report > ./perf.data.report
root:/# cat ./perf.data.report
# To display the perf.data header info, please use --header/--header-only options.
#
#
# Total Lost Samples: 0
#
# Samples: 62K of event 'block:block_rq_issue'
# Event count (approx.): 62359
#
# Overhead Command Shared Object Symbol
# ........ ............... ................. ........................
#
51.22% kworker/1:1H-kb [kernel.kallsyms] [k] blk_mq_start_request
19.99% jbd2/sdcw7-8 [kernel.kallsyms] [k] blk_mq_start_request
19.99% perf [kernel.kallsyms] [k] blk_mq_start_request
3.69% kworker/2:1H-kb [kernel.kallsyms] [k] blk_mq_start_request
3.27% kworker/3:1H-kb [kernel.kallsyms] [k] blk_mq_start_request
1.83% kworker/0:1H-kb [kernel.kallsyms] [k] blk_mq_start_request
# Samples: 0 of event 'dummy:HG'
# Event count (approx.): 0
#
# Overhead Command Shared Object Symbol
# ........ ....... ............. ......
#
#
# (Cannot load tips.txt file, please install perf!)
#
我们再看一个增加了栈分析的例子，过程类似，就是record时加了-g参数：
root:/# perf record -e block:block_rq_issue -e block:block_rq_issue -g
^C[ perf record: Woken up 0 times to write data ]
[ perf record: Captured and wrote 5.660 MB perf.data (19394 samples) ]
# 文本查看，有栈信息了
root:/# perf script > ./perf.data.script
root:/# head ./perf.data.script
perf 16560 [003] 11077.469077: block:block_rq_issue: 70,64 WS 4096 () 3922080 + 8 [perf]
ffffffffb1372e8c blk_mq_start_request+0x9c ([kernel.kallsyms])
ffffffffb1372e8c blk_mq_start_request+0x9c ([kernel.kallsyms])
ffffffffb167886c scsi_queue_rq+0x2dc ([kernel.kallsyms])
ffffffffb1375687 blk_mq_dispatch_rq_list+0x2d7 ([kernel.kallsyms])
ffffffffb137a9e3 __blk_mq_do_dispatch_sched+0x233 ([kernel.kallsyms])
ffffffffb137ad8a __blk_mq_sched_dispatch_requests+0x15a ([kernel.kallsyms])
ffffffffb137af54 blk_mq_sched_dispatch_requests+0x34 ([kernel.kallsyms])
ffffffffb1373007 __blk_mq_run_hw_queue+0x57 ([kernel.kallsyms])
ffffffffb1373197 __blk_mq_delay_run_hw_queue+0x107 ([kernel.kallsyms])
# 输出结果中，有比较详细的各个函数占据的比例
root:/# perf report > ./perf.data.report
root:/# cat ./perf.data.report
# To display the perf.data header info, please use --header/--header-only options.
#
#
# Total Lost Samples: 0
#
# Samples: 19K of event 'block:block_rq_issue'
# Event count (approx.): 19394
#
# Children Self Command Shared Object Symbol
# ........ ........ ............... .................. ....................................
#
45.07% 45.07% kworker/1:1H-kb [kernel.kallsyms] [k] blk_mq_start_request
|
---ret_from_fork
kthread
worker_thread
process_one_work
|
--45.03%--blk_mq_requeue_work
blk_mq_run_hw_queues
blk_mq_run_hw_queue
__blk_mq_delay_run_hw_queue
__blk_mq_run_hw_queue
blk_mq_sched_dispatch_requests
__blk_mq_sched_dispatch_requests
blk_mq_dispatch_rq_list
scsi_queue_rq
blk_mq_start_request
blk_mq_start_request
45.07% 0.00% kworker/1:1H-kb [kernel.kallsyms] [k] ret_from_fork
|
---ret_from_fork
kthread
worker_thread
process_one_work
|
--45.03%--blk_mq_requeue_work
blk_mq_run_hw_queues
blk_mq_run_hw_queue
__blk_mq_delay_run_hw_queue
__blk_mq_run_hw_queue
blk_mq_sched_dispatch_requests
__blk_mq_sched_dispatch_requests
blk_mq_dispatch_rq_list
scsi_queue_rq
blk_mq_start_request
blk_mq_start_request
KernelShark
KernelShark是基于trace-cmd的时序分析工具，使用例子如下。
先使用trace-cmd命令来记录数据，起了4个dd进程来作为分析的对象：
root:/# trace-cmd record -e sched_switch & sleep 5; \
> dd if=/dev/random of=/dev/random & sleep 5; \
> dd if=/dev/random of=/dev/random & sleep 5; \
> dd if=/dev/random of=/dev/random & sleep 5; \
> dd if=/dev/random of=/dev/random & sleep 5; \
> killall dd; sleep 1; echo done; fg %1
Hit Ctrl^C to stop recording
log_data_trans:370.no possible file
done
trace-cmd record -e sched_switch -m 65536
^CCPU0 data recorded at offset=0x67f000
53248 bytes in size
CPU1 data recorded at offset=0x68c000
118784 bytes in size
CPU2 data recorded at offset=0x6a9000
36864 bytes in size
CPU3 data recorded at offset=0x6b2000
94208 bytes in size
[6]+ Terminated dd if=/dev/random of=/dev/random
[5]+ Terminated dd if=/dev/random of=/dev/random
[4]+ Terminated dd if=/dev/random of=/dev/random
[3]+ Terminated dd if=/dev/random of=/dev/random
得到trace.dat文件后，使用KernelShark来分析：
root:/# kernelshark trace.dat
会出现一个图形界面：
每个cpu有一条横轴，轴上就是不同时间点上该cpu上运行的进程，以及触发的事件。判断当前运行的是哪个进程是通过sched_switch这个event来进行的，切换进程时都会执行到这个event。
上图可能不太清楚，我们再通过filter过滤一下，只保留4个dd进程：
可以清楚的看到各个4个进程的启动时序，以及任务在cpu之间的切换过程，如果需要时序分析，而不仅仅是统计数据，那么就比较适合用这个工具了。
今天的文章linux tracers使用介绍分享到此就结束了，感谢您的阅读。
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