Message-ID: <1340280264.18025.4.camel@twins>
Subject: Re: [PATCH 0/4] cputime: Virtual cputime accounting small cleanups
 and consolidation
From: Peter Zijlstra <peterz@infradead.org>
To: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>, Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, Tony Luck <tony.luck@intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Venkatesh Pallipadi <venki@google.com>
Date: Thu, 21 Jun 2012 14:04:24 +0200
In-Reply-To: <20120621095806.36df58f2@de.ibm.com>
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On Thu, 2012-06-21 at 09:58 +0200, Martin Schwidefsky wrote:
> On Thu, 21 Jun 2012 02:46:29 +0200
> Frederic Weisbecker <fweisbec@gmail.com> wrote:
> 
> > 2012/6/21 Peter Zijlstra <peterz@infradead.org>:
> > > On Tue, 2012-06-19 at 15:43 +0200, Frederic Weisbecker wrote:
> > >>
> > >> I wish we could do more vtime cputime accounting consolidation
> > >> but archs do the things pretty differently although I bet the
> > >> behaviour could be more unified.
> > >>
> > > Yes.. so s390,ia64 use thread_info, ppc uses their paca (arch private
> > > precursor to per-cpu data).
> 
> s390 uses the prefix page / lowcore to accumulate some accounting information.
> Which basically is per-cpu data with the advantage that it is accessible with
> at address 0-8191 for each cpu. The entry code does not have to load a pointer
> to get to that page, I would prefer NOT to use per-cpu data here.

Yeah, same for ppc and their paca, I just meant to put the data in
per-cpu (your lowcore and ppc's paca qualify) storage instead of
per-task.

But seeing as I completely overlooked the per-task accounting this
doesn't matter anyway.

There being the per-task accounting also completely wrecks the proposal
I outlined. That only works if its only per-cpu accounting.

The alternative is going full 64bit ns and having the tick fallback do
TICK_NSEC increments. 32bit args that don't do VIRT_TIME or IRQ_TIME
won't like that though :/

So yeah, I did miss something obvious.. no cookies for me.
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