Date: Wed, 4 Jan 2006 15:01:39 -0800
From: Andrew Morton <akpm@osdl.org>
To: Chuck Ebbert <76306.1226@compuserve.com>
Cc: linux-kernel@vger.kernel.org, torvalds@osdl.org,
       Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Subject: Re: [patch 2.6.15] i386: Optimize local APIC timer interrupt code
Message-Id: <20060104150139.34829833.akpm@osdl.org>
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Chuck Ebbert <76306.1226@compuserve.com> wrote:
>
> Local APIC timer interrupt happens HZ times per second on each CPU.
> 
> Optimize it for the case where profile multiplier equals one and does
> not change (99+% of cases); this saves about 20 CPU cycles on Pentium II.
> 
> Also update the old multiplier immediately after noticing it changed,
> while values are register-hot, saving eight bytes of stack depth.

The code which you're patching is cheerfully nuked by a patch in Andi's
tree:
ftp://ftp.firstfloor.org/pub/ak/x86_64/quilt-current/patches/no-subjiffy-profile

I don't immediately understand that patch and I don't recall seeing it
discussed - maybe I was asleep.

It removes the profile multiplier (readprofile -M).  I've used that
occasionally, but can't say that I noticed much benefit from it.

What's the thinking here?
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