linux-kernel - Re: [PATCH 47/48] perf record: Spread maps for --threads option

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Date:   Sun, 23 Sep 2018 21:44:32 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Namhyung Kim <namhyung@...nel.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>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andi Kleen <andi@...stfloor.org>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        kernel-team@....com
Subject: Re: [PATCH 47/48] perf record: Spread maps for --threads option

On Mon, Sep 17, 2018 at 08:40:48PM +0900, Namhyung Kim wrote:
> On Thu, Sep 13, 2018 at 02:54:49PM +0200, Jiri Olsa wrote:
> > Currently we assign all maps to main thread. Adding
> > code that spreads maps for --threads option.
> > 
> > For --thread option we create as many threads as there
> > are memory maps in evlist, which is the number of CPUs
> > in the system or CPUs we monitor. Each thread gets a
> > single data mmap to read.
> > 
> > In addition we have also same amount of tracking mmaps
> > for auxiliary events which we don't create special thread
> > for. Instead we assign the to the main thread, because
> > there's not much traffic expected there.
> > 
> > The assignment is visible from --thread-stats output:
> > 
> >           pid      write       poll       skip  maps (size 20K)
> >     1s   9770       144B          1          0   19K   19K   19K   18K   19K
> >          9772         0B          1          0   18K
> >          9773         0B          1          0   19K
> >          9774         0B          1          0   19K
> > 
> > There are 5 maps for thread 9770 (1 data map and 4 auxiliary)
> > and one data map for every other thread. Each thread writes
> > data to the separate data file.
> 
> Hmm.. not sure it'll work well for large machines with 1000+ cpus.
> What about giving each thread a data mmap and a tracking mmap?

well currently we store the tracking data in single file,
thats why we need just one thread to write them down

with the *_time API, we should be able to properly read the
tracking data separately for each cpu

jirka