linux-kernel - Re: [PATCH 1/3] perf tools: Cache register accesses for unwind processing

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1398690175.1724.5.camel@leonhard>
Date:	Mon, 28 Apr 2014 22:02:55 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Jean Pihet <jean.pihet@...aro.org>
Subject: Re: [PATCH 1/3] perf tools: Cache register accesses for unwind
 processing

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?

Thanks,
Namhyung


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/