linux-kernel - Re: [PATCH RFC 3/3] x86: use mwait for trigger API

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Message-ID: <48A74BAA.4010908@goop.org>
Date:	Sat, 16 Aug 2008 14:50:34 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>, Jens Axboe <jens.axboe@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH RFC 3/3] x86: use mwait for trigger API

Arjan van de Ven wrote:
> monitor/mwait is rather really expensive.. are we really sure we want
> to use this?
> (from an Intel cpu perspective the answer is very likely no; but I don't
> know what AMD does here)
>   

The intended use is when you're going to be waiting for a while (on the
order of microseconds or more).  In the Xen case, I use this to block
the vcpu if we pass a few iterations without the condition being true. 
While the mwait patch doesn't do this at present, it could.

    J

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