linux-kernel - Re: [PATCH V2 0/6][RFC] futex: FUTEX_LOCK with optional adaptive spinning

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Message-ID: <4BBC191F.2090801@redhat.com>
Date:	Wed, 07 Apr 2010 08:33:19 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Darren Hart <dvhltc@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Eric Dumazet <eric.dumazet@...il.com>,
	"Peter W. Morreale" <pmorreale@...ell.com>,
	Rik van Riel <riel@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Sven-Thorsten Dietrich <sdietrich@...ell.com>,
	Chris Mason <chris.mason@...cle.com>,
	John Cooper <john.cooper@...rd-harmonic.com>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [PATCH V2 0/6][RFC] futex: FUTEX_LOCK with optional adaptive
 spinning

On 04/06/2010 10:31 PM, Thomas Gleixner wrote:
>
>> That gives you something along the lines of
>>
>> 	runaddr = find_run_flag(lock);
>> 	do {
>> 		while(*runaddr == RUNNING) {
>> 			if (trylock(lock))
>> 				return WHOOPEE;
>> 			cpu relax
>> 		}
>> 		yield (_on(thread));
>>      
> That would require a new yield_to_target() syscall, which either
> blocks the caller when the target thread is not runnable or returns an
> error code which signals to go into the slow path.
>    

Note, directed yield is something that kvm wants for its own ends.  As 
an internal kernel api, not a syscall, but it's apparently useful.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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