linux-kernel - Re: [PATCH 0/6] x86-64: Micro-optimize vclock

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Date:	Tue, 29 Mar 2011 08:27:06 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andy Lutomirski <luto@....edu>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	John Stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 0/6] x86-64: Micro-optimize vclock_gettime


* Andy Lutomirski <luto@....edu> wrote:

> This series speeds up vclock_gettime(CLOCK_MONOTONIC) on by almost 30%
> (tested on Sandy Bridge).  They're ordered in roughly decreasing order
> of improvement.
> 
> These are meant for 2.6.40, but if anyone wants to take some of them
> for 2.6.39 I won't object.
> 
> The changes and timings (fastest of 20 trials of 100M iters on Sandy
> Bridge) are:
> 
> Unpatched:
> 
> CLOCK_MONOTONIC: 22.09ns
> CLOCK_REALTIME_COARSE: 4.23ns
> CLOCK_MONOTONIC_COARSE: 5.65ns

  [ Patched: ]

> CLOCK_MONOTONIC: 15.66ns
> CLOCK_REALTIME_COARSE: 3.44ns
> CLOCK_MONOTONIC_COARSE: 4.23ns

That looks like a nice speedup, and speedups are definitely welcome. Many of 
your speedup patches were framed in an unclean or hard to maintain fashion 
though - so those have to be improved for this series to become palatable.

Thanks,

	Ingo
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