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Date: Sat, 30 Jan 2016 15:20:39 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Rik van Riel <riel@redhat.com>
Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@kernel.org,
        peterz@infradead.org, luto@amacapital.net,
        Clark Williams <williams@redhat.com>
Subject: Re: [PATCH 2/2] sched,time: call __acct_update_integrals once a jiffy
Message-ID: <20160130142037.GA32581@lerouge>
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 <56ABEB10.5060307@redhat.com>
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On Fri, Jan 29, 2016 at 05:43:28PM -0500, Rik van Riel wrote:
> On 01/29/2016 05:23 PM, riel@redhat.com wrote:
> > From: Rik van Riel <riel@redhat.com>
> 
> > This speeds up
> 
> ... ok, that changelog got truncated :(
> 
> Here is the full version:
> 
> 
> Because __acct_update_integrals does nothing unless the time
> interval in question exceeds a jiffy, there is no real reason
> to call it more than once a jiffy from the syscall, irq, and
> guest entry & exit paths.
> 
> If tasks get rescheduled frequently, the scheduler will still
> update their time statistics normally.
> 
> However, longer running tasks with frequent syscall, irq,
> or guest entry & exit see a difference with this patch.
> 
> A microbenchmark calling an invalid syscall number 10 million
> times in a row speeds up an additional 30% over the numbers
> with just the previous patch, for a total speedup of about 40%
> over 4.4 and 4.5-rc1.
> 
> Run times for the microbenchmark:
> 
> 4.4                             3.8 seconds
> 4.5-rc1                         3.7 seconds
> 4.5-rc1 + first patch           3.3 seconds
> 4.5-rc1 + both patches          2.3 seconds

Very nice improvement!