Messages in this thread | | | From | Arnaldo Carvalho de Melo <> | Date | Mon, 11 Nov 2019 11:04:50 -0300 | Subject | Re: [PATCH v2 1/4] perf probe: Generate event name with line number |
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Em Fri, Nov 08, 2019 at 01:27:58AM +0900, Masami Hiramatsu escreveu: > Generate event name from function name with line number > as <function>_L<line_number>. Note that this is only for > the new event which is defined by the line number of > function (except for line 0). > > If there is another event on same line, you have to use > "-f" option. In that case, the new event has "_1" suffix. > > e.g. > # perf probe -a kernel_read:1 > Added new events: > probe:kernel_read_L1 (on kernel_read:1)
While testing this, using the same function (kernel_read), I found it confusing that it is possible to insert probes in lines seemingly with no code, for instance:
[root@quaco ~]# perf probe -a kernel_read:1 Added new event: probe:kernel_read_L1 (on kernel_read:1)
You can now use it in all perf tools, such as:
perf record -e probe:kernel_read_L1 -aR sleep 1
[root@quaco ~]# perf probe -a kernel_read:2 Added new event: probe:kernel_read_L2 (on kernel_read:2)
You can now use it in all perf tools, such as:
perf record -e probe:kernel_read_L2 -aR sleep 1
[root@quaco ~]# [root@quaco ~]# perf probe --list probe:kernel_read_L1 (on kernel_read@fs/read_write.c) probe:kernel_read_L2 (on kernel_read:1@fs/read_write.c) [root@quaco ~]# perf probe -L kernel_read <kernel_read@/usr/src/debug/kernel-5.3.fc30/linux-5.3.8-200.fc30.x86_64/fs/read_write.c:0> 0 ssize_t kernel_read(struct file *file, void *buf, size_t count, loff_t *pos) 1 { 2 mm_segment_t old_fs; 3 ssize_t result;
5 old_fs = get_fs(); 6 set_fs(KERNEL_DS); /* The cast to a user pointer is valid due to the set_fs() */ 8 result = vfs_read(file, (void __user *)buf, count, pos); 9 set_fs(old_fs); 10 return result; } EXPORT_SYMBOL(kernel_read);
[root@quaco ~]#
What is the point of putting a probe on line 2? I is not initializing, etc, 1 as well, notthing there and we already have 0 (or not specifying a line number) to put a probe at the start of a function, can you clarify?
I'll apply this patch, the problem above isn't strictly related to it.
- Arnaldo
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