From: Masami Hiramatsu <mhiramat@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Axel Rasmussen" <axelrasmussen@google.com>,
"Steven Rostedt" <rostedt@goodmis.org>,
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Subject: Re: [PATCH v2 0/7] Add histogram measuring mmap_lock contention latency
Date: Sat, 30 May 2020 00:03:59 +0900 [thread overview]
Message-ID: <20200530000359.519f38720ab457435ecf7b6f@kernel.org> (raw)
In-Reply-To: <20200529080957.GI706495@hirez.programming.kicks-ass.net>
On Fri, 29 May 2020 10:09:57 +0200
Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, May 28, 2020 at 06:39:08PM -0700, Axel Rasmussen wrote:
>
> > The use case we have in mind for this is to enable this instrumentation
> > widely in Google's production fleet. Internally, we have a userspace thing
> > which scrapes these metrics and publishes them such that we can look at
> > aggregate metrics across our fleet. The thinking is that mechanisms like
> > lockdep or getting histograms with e.g. BPF attached to the tracepoint
> > introduces too much overhead for this to be viable. (Although, granted, I
> > don't have benchmarks to prove this - if there's skepticism, I can produce
> > such a thing - or prove myself wrong and rethink my approach. :) )
>
> Whichever way around; I don't believe in special instrumentation like
> this. We'll grow a thousand separate pieces of crap if we go this route.
>
> Next on, someone will come and instrument yet another lock, with yet
> another 1000 lines of gunk.
>
> Why can't you kprobe the mmap_lock things and use ftrace histograms?
+1.
As far as I can see the series, if you want to make a histogram
of the duration of acquiring locks, you might only need 7/7 (but this
is a minimum subset.) I recommend you to introduce a set of tracepoints
-- start-locking, locked, and released so that we can investigate
which process is waiting for which one. Then you can use either bpf
or ftrace to make a histogram easily.
Thank you,
--
Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2020-05-29 15:05 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-28 23:52 Axel Rasmussen
2020-05-29 0:24 ` Steven Rostedt
2020-05-29 1:39 ` Axel Rasmussen
2020-05-29 8:09 ` Peter Zijlstra
2020-05-29 15:03 ` Masami Hiramatsu [this message]
2020-05-29 22:38 ` Axel Rasmussen
2020-05-29 5:32 ` Thomas Gleixner
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