linux-kernel - Re: [2.6.39-rc2] perf top fails to mmap

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Date:	Wed, 6 Apr 2011 21:13:11 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	David Ahern <dsahern@...il.com>
Cc:	Tim Blechmann <tim@...ngt.org>, linux-kernel@...r.kernel.org
Subject: Re: [2.6.39-rc2] perf top fails to mmap - bisected to 70db7533

Em Wed, Apr 06, 2011 at 04:45:09PM -0600, David Ahern escreveu:
> On 04/06/11 16:15, David Ahern wrote:
> > On 04/06/11 14:48, Tim Blechmann wrote:
> >>>>> this happens when running perf as the same process as the process and
> >>>>> when running perf as root.
> >>>
> >>> yep, works for me as well:
> >>>
> >>> [acme@...lia ~]$ cat vsyscall.c
> >>
> >> after including unistd.h, this compiles and works fine. however i cannot profile 
> >> any multithreaded program. does this work for you?

> > That does fail:
> > # ps -C rsyslogd -L
> >   PID   LWP TTY          TIME CMD
> >   795   795 ?        00:00:00 rsyslogd
> >   795   797 ?        00:00:00 rsyslogd
> >   795   798 ?        00:00:00 rsyslogd

> > # /tmp/build-perf/perf top -p 795
> > Failed to mmap with 22 (Invalid argument)

> > strace shows it failing at:
> > ioctl(4, PERF_EVENT_IOC_SET_OUTPUT, 0x3) = -1 EINVAL (Invalid argument)

> > Changing to use thread only works:
> > # /tmp/build-perf/perf top -t 795
> 
> git bisect points to:
> 
> 70db7533caef02350ec8d6852e589491bca3a951 is the first bad commit
> commit 70db7533caef02350ec8d6852e589491bca3a951
> Author: Arnaldo Carvalho de Melo <acme@...hat.com>
> Date:   Wed Jan 12 22:39:13 2011 -0200
> 
> perf evlist: Move the mmap array from perf_evsel
> 
> Adopting the new model used in 'perf record', where we don't have a map
> per thread per cpu, instead we have an mmap per cpu, established on the
> first fd for that cpu and ask the kernel using the
> PERF_EVENT_IOC_SET_OUTPUT ioctl to send events for the other fds on that
> cpu for the one with the mmap.
> 
> The methods moved from perf_evsel to perf_evlist, but for easing review
> they were modified in place, in evsel.c, the next patch will move the
> migrated methods to evlist.c.
> 
> With this 'perf top' now uses the same mmap model used by 'perf record'
> and the next patches will make 'perf record' use these new routines,
> establishing a common codebase for both tools.
> 
> ----------
> 
> Coincidentally, perf-record is also broken. git bisect points to:
> 
> dd7927f4f8ee75b032ff15aeef4bda49719a443a is the first bad commit
> commit dd7927f4f8ee75b032ff15aeef4bda49719a443a
> Author: Arnaldo Carvalho de Melo <acme@...hat.com>
> Date:   Wed Jan 12 14:28:51 2011 -0200
> 
> perf record: Use perf_evsel__open
> 
> Now its time to factor out the mmap handling bits into the perf_evsel
> class.

I'll work on that tomorrow, if nobody fixes this till then :-)

- Arnaldo
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