linux-kernel - Re: [PATCH][RFC] Adding information of counts processes acquired how many spinlocks to schedstat

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Date:	Wed, 1 Jul 2009 17:44:51 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Hitoshi Mitake <mitake@....info.waseda.ac.jp>
Cc:	mingo@...e.hu, acme@...hat.com, a.p.zijlstra@...llo.nl,
	andi@...stfloor.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][RFC] Adding information of counts processes acquired
	how many spinlocks to schedstat

On Wed, Jul 01, 2009 at 09:53:04PM +0900, Hitoshi Mitake wrote:
> From: Ingo Molnar <mingo@...e.hu>
> Subject: Re: [PATCH][RFC] Adding information of counts processes acquired how many spinlocks to schedstat
> Date: Wed, 1 Jul 2009 13:06:20 +0200
> 
> > 
> > * Hitoshi Mitake <mitake@....info.waseda.ac.jp> wrote:
> > 
> > > From: Ingo Molnar <mingo@...e.hu>
> > > Subject: Re: [PATCH][RFC] Adding information of counts processes acquired how many spinlocks to schedstat
> > > Date: Wed, 1 Jul 2009 11:07:49 +0200
> > > 
> > > > 
> > > > * Hitoshi Mitake <mitake@....info.waseda.ac.jp> wrote:
> > > > 
> > > > > From: Andi Kleen <andi@...stfloor.org>
> > > > > Subject: Re: [PATCH][RFC] Adding information of counts processes acquired how many spinlocks to schedstat
> > > > > Date: Wed, 01 Jul 2009 09:38:04 +0200
> > > > > 
> > > > > > Hitoshi Mitake <mitake@....info.waseda.ac.jp> writes:
> > > > > > 
> > > > > > > Hi,
> > > > > > >
> > > > > > > I wrote a test patch which add information of counts processes acquired how many spinlocks to schedstat.
> > > > > > > After applied this patch, /proc/<PID>/sched will change like this,
> > > > > > 
> > > > > > The problem is that spinlocks are very common and schedstats is 
> > > > > > enabled commonly in production kernels. You would need to 
> > > > > > demonstrate that such a change doesn't have significant 
> > > > > > performance impact. For me it looks like it has.
> > > > > 
> > > > > I agree with your opinion about performance impact.
> > > > > I thought this will make no problem,
> > > > > because schedstat is categorized as "Kernel hacking" section.
> > > > > But according to you, many production kernels enable it
> > > > > so my patch will make widespread performance degradation.
> > > > > I didn't know that, sorry.
> > > > 
> > > > His arguments are bogus: both lockstat and perfcounters are optional 
> > > > (and default off), and the sw counter can be made near zero cost 
> > > > even if both perfcounters and lockstat is enabled. Also, sw counters 
> > > > are generally per CPU, etc. so not a performance issue.
> > > > 
> > > > The only (small) overhead will be when the lock-acquire sw counter 
> > > > is actively enabled because you run 'perf stat -e lock-acquire' - 
> > > > but that is expected and inherent in pretty much any kind of 
> > > > instrumentation.
> > > > 
> > > > The feature you are working on has the chance to be a very useful 
> > > > and popular piece of instrumentation. Being able to tell the lock 
> > > > acquire stats on a per task, per workload, per CPU or system-wide 
> > > > basis is a unique capability no other tool can offer right now.
> > > > 
> > > > Andi is often trolling perfcounters related (and other) threads, 
> > > > please dont let yourself be deterred by that and feel free to ignore 
> > > > him.
> > > OK, at least it is truth that
> > > counter in perfcounters makes only valid overhead.
> > > 
> > > And I have a question,
> > > I tried to build perf, but I got a build error,
> > > 
> > > util/symbol.c: In function ‘dso__load_sym’:
> > > util/symbol.c:466: error: ‘ELF_C_READ_MMAP’ undeclared (first use in this function)
> > > util/symbol.c:466: error: (Each undeclared identifier is reported only once
> > > util/symbol.c:466: error: for each function it appears in.)
> > > 
> > > I used this libelf,
> > > http://www.mr511.de/software/english.html
> > > but constant ELF_C_READ_MMAP is not provided...
> > > 
> > > which "libelf" should I use?
> > > It seems that there are some libelf implementations.
> > 
> > I use the elfutils-libelf* packages:
> > 
> >  elfutils-libelf-devel-static-0.141-1.fc10.i386
> >  elfutils-0.141-1.fc10.i386
> >  elfutils-libelf-0.141-1.fc10.i386
> >  elfutils-libs-0.141-1.fc10.i386
> >  elfutils-libelf-devel-0.141-1.fc10.i386
> > 
> > do they work fine or you?
> 
> I'm a Debian user, so I build this library from source
> 
> https://fedorahosted.org/releases/e/l/elfutils/elfutils-0.141.tar.bz2
> 
> And I succeed to build perf, thanks!


You could also just

apt-get install libelf-dev

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