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Date: Mon, 18 Jan 2010 20:55:27 +1100
From: Anton Blanchard <anton@samba.org>
To: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Bharata B Rao <bharata@linux.vnet.ibm.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Ingo Molnar <mingo@elte.hu>, Balbir Singh <balbir@linux.vnet.ibm.com>,
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       tglx@linutronix.de, kamezawa.hiroyu@jp.fujitsu.com,
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       Fenghua Yu <fenghua.yu@intel.com>,
       Heiko Carstens <heiko.carstens@de.ibm.com>, linux390@de.ibm.com
Subject: Re: [PATCH] sched: cpuacct: Use bigger percpu counter batch values
 for stats counters
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Hi Martin,

> For s390 the jiffies_to_cputime is a compile time constant. No need to
> initialize it at runtime, no? 

Indeed it is, I didn't look closely enough. Same with ia64 so no work to
do on either arch :)

> The patch itself trades some accuracy (larger cpu accounting value that
> are stored per-cpu) against runtime overhead (spinlock to transfer the
> value to the global variable in __percpu_counter_add). Did you
> calculate how big the loss in accuracy is?

The idea is we are already batching percpu_counter_batch jiffies, so
with CONFIG_VIRT_CPU_ACCOUNTING we batch the equivalent amount in
cputime.

Anton