linux-kernel - Re: [PATCH] perf stat: Do not show stats if workload fails

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Message-ID: <20131226141507.GD30980@ghostprotocols.net>
Date:	Thu, 26 Dec 2013 11:15:07 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	David Ahern <dsahern@...il.com>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] perf stat: Do not show stats if workload fails

Em Thu, Dec 26, 2013 at 09:11:22AM -0500, David Ahern escreveu:
> On 12/24/13, 8:30 AM, Arnaldo Carvalho de Melo wrote:
> >Em Tue, Dec 24, 2013 at 09:53:42AM -0300, Arnaldo Carvalho de Melo escreveu:
> >>>The thing to check is perf_evlist__{prepare,start}_workload notification
> >>>errors using SIGUSR1, that we need to check for in the caller, and emit
> >>>the message, no?
> >Something like this:
> >
> >1. We tell perf_evlist__prepare_workload that we want a signal if execvp
> >fails, it will be a SIGUSR1
> >
> >2. We catch that signal in 'stat' and check that we got a signal, only
> >problem so far with this signal maze is that we're getting a SIGCHLD
> >while I was expecting a SIGUSR1... I.e. the "if (signr != -1) test
> >really should be if (signr == SIGUSR1), but I'm getting a SIGCHLD there
> >and the elves are tugging me away...
> 
> Did the elves release you?
> 
> There are all kinds of failure paths with the workload functions. In
> the end I was focusing on perf-stat actually checking the rc on the
> start_workload function. If it fails, then write() failed and
> something happened to the workload process. In that case don't show
> the counters.
> 
> Handling the other error paths with appropriate messages will take
> additional effort - as you are finding. ;-)

Right, but I can't apply that patch, as it makes 'perf stat
whatever-workload' to fail, as I realized when doing a demo to someone
interested in using perf ;-\

So for now I'm not applying that one.

Ah, at this point elves are everywhere, dammit! ;-)

- Arnaldo
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