Em Tue, Sep 09, 2014 at 05:03:53PM -0700, Andi Kleen escreveu:
> From: Andi Kleen <[email protected]>
>
> It's currently difficult to filter out perf itself using a filter.
> This can give cascading effects during IO tracing when the IO
> perf does itself causes more trace output.
>
> The best way to filter is to use the pid. But it's difficult to get the pid
> of perf without using hacks.
>
> Add a PERF_PID meta variable to the perf filter that contains the current pid.
>
> With this patch the following works
>
> % perf record -e syscalls:sys_enter_write -a --filter 'common_pid !=
> PERF_PID' ...
>
> This won't work for more complex perf pipe lines with multiple processes,
> but at least solves the problem nicely for a single perf.
> @@ -983,6 +984,13 @@ int parse_filter(const struct option *opt, const char
> *str,
> return -1;
> }
>
> + /* Assume a pid has not more than 8 characters */
> + pid = strstr(last->filter, "PERF_PID");
> + if (pid) {
> + char buf[9];
> + snprintf(buf, 9, "%8d", getpid());
> + memcpy(pid, buf, 8);
Can we please remove this assumption?
If the get to be more than 8 chars we'll be just truncating stuff and
possibly filtering some other, unrelated process, no?
pid_t getpid(void);
typedef __pid_t pid_t;
__STD_TYPE __PID_T_TYPE __pid_t; /* Type of process identifications. */
/usr/include/bits/typesizes.h:#define __PID_T_TYPE __S32_TYPE
/usr/include/bits/types.h:#define __S32_TYPE int
[acme@zoo linux]$ uname -a
Linux zoo.ghostprotocols.net 3.17.0-rc1+ #2 SMP Thu Aug 21 12:25:42 BRT 2014
x86_64 x86_64 x86_64 GNU/Linux
[acme@zoo ~]$ cat a.c
#include <limits.h>
#include <stdio.h>
int main(int argc, char *argv[])
{
printf("%8d", INT_MAX);
}
[acme@zoo ~]$ make a
cc a.c -o a
[acme@zoo ~]$ ./a | wc -c
10
[acme@zoo ~]$
The feature is needed, no doubt about it, thanks for working on it.
I guess we need the equivalent of (python regexp) s/PERF_PID/("%d" % getpid())/g
to properly implement this.
- Arnaldo
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