linux-kernel - Re: [PATCH 1/8] perf: Allow to block process in syscall tracepoints

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Message-ID: <20181208104423.GE5289@hirez.programming.kicks-ass.net>
Date:   Sat, 8 Dec 2018 11:44:23 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Luis Claudio R. Goncalves" <lclaudio@...g.org>, ldv@...linux.org,
        esyr@...hat.com, Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 1/8] perf: Allow to block process in syscall tracepoints

On Fri, Dec 07, 2018 at 03:14:33PM -0500, Steven Rostedt wrote:
> On Fri, 7 Dec 2018 16:11:05 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Fri, Dec 07, 2018 at 08:41:18AM -0500, Steven Rostedt wrote:
> > > On Fri, 7 Dec 2018 09:58:39 +0100
> > > Peter Zijlstra <peterz@...radead.org> wrote:
> > >   
> > > > These patches give no justification *what*so*ever* for why we're doing
> > > > ugly arse things like this. And why does this, whatever this is, need to
> > > > be done in perf?
> > > > 
> > > > IOW, what problem are we solving ?  
> > > 
> > > I guess the cover letter should have had a link (or copy) of this:
> > > 
> > >  http://lkml.kernel.org/r/20181128134700.212ed035@gandalf.local.home  
> > 
> > That doesn't even begin to explain. Who cares about strace and why? And
> > why is it such a bad thing to loose the occasional record etc..
> 
> Who cares about strace? Do I really need to answer that? It's one of
> the most used tools for seeing what a program is doing.

It's a tool I haven't used in years, given we have so many better tools
around these days.

> Why do we care about lost events? Because strace records *all* events,
> as that's what it does and that's what it always has done. It would be
> a break in functionality (a regression) if it were to start losing
> events. I use strace to see everything that an application is doing.

So make a new tool; break the expectation of all events. See if there's
anybody that really cares.

> When we discussed this at plumbers, Oracle people came to me and said
> how awesome it would be to run strace against their database accesses.
> The problem today is that strace causes such a large overhead that it
> isn't feasible to trace any high speed applications, especially if
> there are time restraints involved.

So have them run that perf thing acme pointed to.

So far nobody's made a good argument for why we cannot have LOST events.