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Date: Mon, 28 Apr 2014 15:24:20 +0200
From: Jiri Olsa <jolsa@redhat.com>
To: Namhyung Kim <namhyung@kernel.org>
Cc: linux-kernel@vger.kernel.org, Corey Ashford <cjashfor@linux.vnet.ibm.com>,
        David Ahern <dsahern@gmail.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Ingo Molnar <mingo@kernel.org>, Paul Mackerras <paulus@samba.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Jean Pihet <jean.pihet@linaro.org>
Subject: Re: [PATCH 1/3] perf tools: Cache register accesses for unwind
 processing
Message-ID: <20140428132420.GD18628@krava.brq.redhat.com>
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On Mon, Apr 28, 2014 at 10:02:55PM +0900, Namhyung Kim wrote:
> Hi Jiri,
> 
> 2014-04-28 (월), 11:48 +0200, Jiri Olsa:
> > On Sun, Apr 27, 2014 at 11:29:21PM +0900, Namhyung Kim wrote:
> > > Hi Jiri,
> > > 
> > > 2014-04-17 (목), 19:39 +0200, Jiri Olsa:
> > > > Caching registers value into an array. Got about 4% speed up
> > > > of perf_reg_value function for report command processing
> > > > dwarf unwind stacks.
> > > 
> > > I'm not familiar with the code base, so probably silly questions:  Where
> > > does the speed up come from?  IOW I don't know what's the difference
> > > between the regs->regs and regs->cached_regs.  And does the cached_regs
> > > contain correct values of registers for each frame?
> > 
> > the current way register's value is accessed is to get its
> > index in the sample's regs array.. based on register's id
> > and the registers mask
> > 
> > so each time you want register value you traverse the registers
> > mask and count reg's index for the sample regs array
> > 
> > this patch does this only once for each register (at the time it's
> > first accessed) and cache its value in the array (cache_regs). The
> > cache_mask is used to identify which regs are already cached.
> 
> That means it'll get the same value everytime it accesses a register in
> frames in a sample?

right..

jirka