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

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Message-Id: <20090701.215304.864843820974206197.mitake@dcl.info.waseda.ac.jp>
Date:	Wed, 01 Jul 2009 21:53:04 +0900 (JST)
From:	Hitoshi Mitake <mitake@....info.waseda.ac.jp>
To:	mingo@...e.hu
Cc:	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

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!