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From: Peter Zijlstra on 18 Dec 2009 16:00
On Fri, 2009-12-18 at 18:42 -0200, Arnaldo Carvalho de Melo wrote:
> From: Arnaldo Carvalho de Melo <acme(a)redhat.com>
>
> IOW: Now 'perf record -a' works, this was a bug introduced in:
>
> 856e96608a72412d319e498a3a7c557571f811bd
> "perf record: Properly synchronize child creation"
>
> Reported-by: Pekka Enberg <penberg(a)cs.helsinki.fi>
> Cc: Frédéric Weisbecker <fweisbec(a)gmail.com>
> Cc: Mike Galbraith <efault(a)gmx.de>
> Cc: Peter Zijlstra <a.p.zijlstra(a)chello.nl>
> Cc: Paul Mackerras <paulus(a)samba.org>
> Signed-off-by: Arnaldo Carvalho de Melo <acme(a)redhat.com>
> ---
> tools/perf/builtin-record.c | 9 +++++----
> 1 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 63136d0..90eedd9 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -402,7 +402,7 @@ static void atexit_header(void)
> perf_header__write(&session->header, output, true);
> }
>
> -static int __cmd_record(int argc __used, const char **argv)
> +static int __cmd_record(int argc, const char **argv)
> {
> int i, counter;
> struct stat st;
> @@ -422,7 +422,8 @@ static int __cmd_record(int argc __used, const char **argv)
> signal(SIGCHLD, sig_handler);
> signal(SIGINT, sig_handler);
>
> - if (pipe(child_ready_pipe) < 0 || pipe(go_pipe) < 0) {
> + if (target_pid == -1 && argc > 0 &&
> + (pipe(child_ready_pipe) < 0 || pipe(go_pipe) < 0)) {
> perror("failed to create pipes");
> exit(-1);
> }

Why bother?

> @@ -483,7 +484,7 @@ static int __cmd_record(int argc __used, const char **argv)
>
> atexit(atexit_header);
>
> - if (target_pid == -1) {
> + if (target_pid == -1 && argc > 0) {
> pid = fork();
> if (pid < 0) {
> perror("failed to fork");

I'd write:

target_pid == -1 && !system_wide

> @@ -667,7 +668,7 @@ int cmd_record(int argc, const char **argv, const char *prefix __used)
>
> argc = parse_options(argc, argv, options, record_usage,
> PARSE_OPT_STOP_AT_NON_OPTION);
> - if (!argc && target_pid == -1 && (!system_wide || profile_cpu == -1))
> + if (!argc && target_pid == -1 && !system_wide)
> usage_with_options(record_usage, options);
>
> symbol__init();

Right, so I was thinking -C would be enough to also start profiling..
clearly messed up the logic though :/

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From: Peter Zijlstra on 18 Dec 2009 16:20
On Fri, 2009-12-18 at 18:58 -0200, Arnaldo Carvalho de Melo wrote:
> Em Fri, Dec 18, 2009 at 09:52:41PM +0100, Peter Zijlstra escreveu:
> > On Fri, 2009-12-18 at 18:42 -0200, Arnaldo Carvalho de Melo wrote:
> > > From: Arnaldo Carvalho de Melo <acme(a)redhat.com>
> > > @@ -422,7 +422,8 @@ static int __cmd_record(int argc __used, const char **argv)
> > > signal(SIGCHLD, sig_handler);
> > > signal(SIGINT, sig_handler);
> > >
> > > - if (pipe(child_ready_pipe) < 0 || pipe(go_pipe) < 0) {
> > > + if (target_pid == -1 && argc > 0 &&
> > > + (pipe(child_ready_pipe) < 0 || pipe(go_pipe) < 0)) {
> > > perror("failed to create pipes");
> > > exit(-1);
> > > }
> >
> > Why bother?
>
> Because we don't need it?

Well its a rare error, and the paranoid in me says bailing asap avoids
funny cases later.

> > > @@ -483,7 +484,7 @@ static int __cmd_record(int argc __used, const char **argv)
> > >
> > > atexit(atexit_header);
> > >
> > > - if (target_pid == -1) {
> > > + if (target_pid == -1 && argc > 0) {
> > > pid = fork();
> > > if (pid < 0) {
> > > perror("failed to fork");
> >
> > I'd write:
> >
> > target_pid == -1 && !system_wide
>
> Because we want this to work:
>
> [root(a)doppio linux-2.6-tip]# perf record -a -f sleep 2
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.243 MB perf.data (~10599 samples) ]
> [root(a)doppio linux-2.6-tip]#
>
> See, no hands mother! I.e. it is system wide, but just for 2 seconds,
> its clever, but I like it, and it always worked :-)

Ah, right.. yes, totally forgot about that.

> > > @@ -667,7 +668,7 @@ int cmd_record(int argc, const char **argv, const char *prefix __used)
> > >
> > > argc = parse_options(argc, argv, options, record_usage,
> > > PARSE_OPT_STOP_AT_NON_OPTION);
> > > - if (!argc && target_pid == -1 && (!system_wide || profile_cpu == -1))
> > > + if (!argc && target_pid == -1 && !system_wide)
> > > usage_with_options(record_usage, options);
> > >
> > > symbol__init();
> >
> > Right, so I was thinking -C would be enough to also start profiling..
> > clearly messed up the logic though :/
>
> Yeah, it should, meaning "profile everything on CPU N"

Right, so I tried folding that in and goofed up.

Anyway, patch looks ok, thanks!

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From: Peter Zijlstra on 18 Dec 2009 16:40
On Fri, 2009-12-18 at 18:58 -0200, Arnaldo Carvalho de Melo wrote:
> > > - if (pipe(child_ready_pipe) < 0 || pipe(go_pipe) < 0) {
> > > + if (target_pid == -1 && argc > 0 &&
> > > + (pipe(child_ready_pipe) < 0 || pipe(go_pipe) < 0)) {
> > > perror("failed to create pipes");
> > > exit(-1);
> > > }

Also, there's an unconditional close() a bit further down.

If not for that, I'd have put the whole mkpipe thing in the if
(target_pid == -1) branch.

Maybe I shouldn't have skimped on the extra state for that close

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From: Ingo Molnar on 18 Dec 2009 17:10

* Peter Zijlstra <peterz(a)infradead.org> wrote:

> > Because we want this to work:
> >
> > [root(a)doppio linux-2.6-tip]# perf record -a -f sleep 2
> > [ perf record: Woken up 1 times to write data ]
> > [ perf record: Captured and wrote 0.243 MB perf.data (~10599 samples) ]
> > [root(a)doppio linux-2.6-tip]#
> >
> > See, no hands mother! I.e. it is system wide, but just for 2 seconds,
> > its clever, but I like it, and it always worked :-)
>
> Ah, right.. yes, totally forgot about that.

I use the 'perf record -a -f sleep 1' trick all the time to capture a
system-wide snippet of a particular workload.

Ingo
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From: Xiao Guangrong on 20 Dec 2009 05:40


Arnaldo Carvalho de Melo wrote:
> From: Arnaldo Carvalho de Melo <acme(a)redhat.com>
>
> IOW: Now 'perf record -a' works, this was a bug introduced in:
>
> 856e96608a72412d319e498a3a7c557571f811bd
> "perf record: Properly synchronize child creation"
>

Sorry, i not noticed this patch and also send a patch to fix this bug,
See:
http://lkml.org/lkml/2009/12/20/7

please ignore my patch.

Thanks,
Xiao
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