linux-kernel - Re: [PATCH v2 11/14] perf report: cache srclines for callchain nodes

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Date:   Thu, 10 Aug 2017 13:51:40 +0200
From:   Milian Wolff <milian.wolff@...b.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     acme@...nel.org, Jin Yao <yao.jin@...ux.intel.com>,
        Linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        David Ahern <dsahern@...il.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>, kernel-team@....com
Subject: Re: [PATCH v2 11/14] perf report: cache srclines for callchain nodes

On Donnerstag, 10. August 2017 04:13:25 CEST Namhyung Kim wrote:
> Hi Milian,
> 
> On Sun, Aug 06, 2017 at 11:24:43PM +0200, Milian Wolff wrote:
> > On one hand this ensures that the memory is properly freed when
> > the DSO gets freed. On the other hand this significantly speeds up
> > the processing of the callchain nodes when lots of srclines are
> > requested. For one of my data files e.g.:
> > 
> > Before:
> >  Performance counter stats for 'perf report -s srcline -g srcline --
stdio':
> >       52496.495043      task-clock (msec)         #    0.999 CPUs utilized
> >       
> >                634      context-switches          #    0.012 K/sec
> >                
> >                  2      cpu-migrations            #    0.000 K/sec
> >            
> >            191,561      page-faults               #    0.004 M/sec
> >    
> >    165,074,498,235      cycles                    #    3.144 GHz
> >    334,170,832,408      instructions              #    2.02  insn per
> >    cycle
> >    
> >     90,220,029,745      branches                  # 1718.591 M/sec
> >     
> >        654,525,177      branch-misses             #    0.73% of all
> >        branches
> >       
> >       52.533273822 seconds time elapsedProcessed 236605 events and lost 40
> >       chunks!> 
> > After:
> >  Performance counter stats for 'perf report -s srcline -g srcline --
stdio':
> >       22606.323706      task-clock (msec)         #    1.000 CPUs utilized
> >       
> >                 31      context-switches          #    0.001 K/sec
> >                 
> >                  0      cpu-migrations            #    0.000 K/sec
> >            
> >            185,471      page-faults               #    0.008 M/sec
> >     
> >     71,188,113,681      cycles                    #    3.149 GHz
> >    
> >    133,204,943,083      instructions              #    1.87  insn per
> >    cycle
> >    
> >     34,886,384,979      branches                  # 1543.214 M/sec
> >     
> >        278,214,495      branch-misses             #    0.80% of all
> >        branches
> >       
> >       22.609857253 seconds time elapsed
> > 
> > Note that the difference is only this large when `--inline` is not
> > passed. In such situations, we would use the inliner cache and
> > thus do not run this code path that often.
> > 
> > I think that this cache should actually be used in other places, too.
> > When looking at the valgrind leak report for perf report, we see tons
> > of srclines being leaked, most notably from calls to
> > hist_entry__get_srcline. The problem is that get_srcline has many
> > different formatting options (show_sym, show_addr, potentially even
> > unwind_inlines when calling __get_srcline directly). As such, the
> > srcline cannot easily be cached for all calls, or we'd have to add
> > caches for all formatting combinations (6 so far). An alternative
> > would be to remove the formatting options and handle that on a
> > different level - i.e. print the sym/addr on demand wherever we
> > actually output something. And the unwind_inlines could be moved into
> > a separate function that does not return the srcline.
> 
> Agreed.  Also I guess no need to unwind anymore to get a srcfile for
> an entry with your change.

Does this mean I should respin the patch series with the above changes 
integrated? Or can we get this in first and then continue with the cleanup as 
described above later on?

Thanks

-- 
Milian Wolff | milian.wolff@...b.com | Senior Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts