From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Jan Beulich <JBeulich@novell.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
"mingo@elte.hu" <mingo@elte.hu>,
"tglx@linutronix.de" <tglx@linutronix.de>,
ksrinivasan <ksrinivasan@novell.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"hpa@zytor.com" <hpa@zytor.com>
Subject: Re: [PATCH 4/4, v2] x86: enlightenment for ticket spin locks - improve yield behavior on Xen
Date: Wed, 30 Jun 2010 12:10:22 +0200 [thread overview]
Message-ID: <4C2B180E.9060104@goop.org> (raw)
In-Reply-To: <4C2B21300200007800008BDC@vpn.id2.novell.com>
On 06/30/2010 10:49 AM, Jan Beulich wrote:
>>>> On 30.06.10 at 10:11, Peter Zijlstra <peterz@infradead.org> wrote:
>>>>
>> On Tue, 2010-06-29 at 15:35 +0100, Jan Beulich wrote:
>>
>>> The (only) additional overhead this introduces for native execution is
>>> the writing of the owning CPU in the lock acquire paths.
>>>
>> Uhm, and growing the size of spinlock_t to 6 (or 8 bytes when aligned)
>> bytes when NR_CPUS>256.
>>
> Indeed, I should have mentioned that. Will do so in an eventual
> next version.
>
Rather than increasing the lock size, why not just disable the
enlightenment if the number of (possible) cpus is > 256? I don't think
a VM will ever have that many cpus, so it will only apply in the case of
booting the kernel on large physical machine.
J
next prev parent reply other threads:[~2010-06-30 10:10 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-29 14:35 [PATCH 4/4, v2] x86: enlightenment for ticket spin locks - improve yield behavior on Xen Jan Beulich
2010-06-30 8:11 ` Peter Zijlstra
2010-06-30 8:49 ` Jan Beulich
2010-06-30 9:24 ` Peter Zijlstra
2010-06-30 10:10 ` Jeremy Fitzhardinge [this message]
2010-06-30 11:25 ` Jan Beulich
2010-06-30 10:08 ` Jeremy Fitzhardinge
2010-06-30 11:22 ` Jan Beulich
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