Re: [PATCH] 2.5: push BKL out of llseek
Russell King (rmk@arm.linux.org.uk)
Wed, 30 Jan 2002 10:36:40 +0000
On Tue, Jan 29, 2002 at 09:20:10PM -0500, Robert Love wrote:
> On Tue, 2002-01-29 at 20:26, Andrew Morton wrote:
> > Just a little word of caution here. Remember the
> > apache-flock-synchronisation fiasco, where removal
> > of the BKL halved Apache throughput on 8-way x86.
> >
> > This was because the BKL removal turned serialisation
> > on a quick codepath from a spinlock into a schedule().
>
> I feared this too, but eventually I decided it was worth it and
> benchmarks backed that up. If nothing else this is yet-another-excuse
> for locks that can spin-then-sleep.
>
> I posted dbench results, which show a positive gain even on 2-way for
> multiple client loads.
Luckily, apache on its own doesn't seem to use lseek() when sending the
file - it seems to be an open, mmap, write. (apache 1.3.22)
However, php with apache does do an lseek on the target script. Now
remember the /. effect... You'll be accessing the same file from
several apache or php processes.
--
Russell King (rmk@arm.linux.org.uk) The developer of ARM Linux
http://www.arm.linux.org.uk/personal/aboutme.html
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