From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Pavel Machek <pavel@ucw.cz>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@osdl.org>,
Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [PATCH 0/6] Per-processor private data areas for i386
Date: Wed, 27 Sep 2006 13:28:20 -0700 [thread overview]
Message-ID: <451ADEE4.4010508@goop.org> (raw)
In-Reply-To: <20060927194600.GA4538@ucw.cz>
Pavel Machek wrote:
> So we have 4% slowdown...
>
Yes, that would be the worst-case slowdown in the hot-cache case.
Rearranging the layout of the GDT would remove any theoretical
cold-cache slowdown (I haven't measured if there's any impact in practice).
> ...and 0.2% smaller kernel. I guess you should demonstrate speedup at
> complex syscalls before wedecide it is worth it...
That would be nice, but this patch series isn't really intended to be a
performance improvement. That would be nice, but the main motivation is
to make inline assembler patching for the paravirt work cleaner.
Rusty and I have also been investigating how to use the %gs-based memory
to implement all percpu data, rather than the few special cases this
patch series currently covers, which will help further amortize the
entry/exit cost.
Rusty has also done more comprehensive benchmarks with his variant of
this patch series, and found no statistically interesting performance
difference. Which is pretty much what I would expect, since it doesn't
increase cache-misses at all.
J
next prev parent reply other threads:[~2006-09-27 20:28 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-09-25 18:45 [PATCH 0/6] Per-processor private data areas for i386 jeremy
2006-09-25 18:45 ` [PATCH 1/6] Initialize the per-CPU data area jeremy
2006-09-25 20:49 ` Andi Kleen
2006-09-25 20:59 ` Jeremy Fitzhardinge
2006-09-25 21:05 ` Andi Kleen
2006-09-25 21:33 ` Jeremy Fitzhardinge
2006-09-25 18:45 ` [PATCH 2/6] Use %gs as the PDA base-segment in the kernel jeremy
2006-09-25 18:45 ` [PATCH 3/6] Fix places where using %gs changes the usermode ABI jeremy
2006-09-25 18:45 ` [PATCH 4/6] Update sys_vm86 to cope with changed pt_regs and %gs usage jeremy
2006-09-25 18:45 ` [PATCH 5/6] Implement smp_processor_id() with the PDA jeremy
2006-09-25 18:45 ` [PATCH 6/6] Implement "current" " jeremy
2006-09-27 19:46 ` [PATCH 0/6] Per-processor private data areas for i386 Pavel Machek
2006-09-27 20:28 ` Jeremy Fitzhardinge
2006-09-27 20:28 ` Jeremy Fitzhardinge [this message]
2006-09-29 0:22 ` Rusty Russell
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