linux-kernel - Re: [PATCH 1/4, v2] x86: enlightenment for ticket spin locks

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Date:	Wed, 30 Jun 2010 10:05:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jan Beulich <JBeulich@...ell.com>
Cc:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	jeremy.fitzhardinge@...rix.com,
	Ky Srinivasan <KSrinivasan@...ell.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4, v2] x86: enlightenment for ticket spin locks -
 base implementation

On Tue, 2010-06-29 at 15:31 +0100, Jan Beulich wrote:
> Add optional (alternative instructions based) callout hooks to the
> contended ticket lock and the ticket unlock paths, to allow hypervisor
> specific code to be used for reducing/eliminating the bad effects
> ticket locks have on performance when running virtualized.

Uhm, I'd much rather see a single alternative implementation, not a
per-hypervisor lock implementation.

> For the moment, this isn't intended to be used together with pv-ops,
> but this is just to simplify initial integration. The ultimate goal
> for this should still be to replace pv-ops spinlocks.

So why not start by removing that?

> +config ENLIGHTEN_SPINLOCKS

Why exactly are these enlightened? I'd say CONFIG_UNFAIR_SPINLOCKS would
be much better.

> +#define X86_FEATURE_SPINLOCK_YIELD (3*32+31) /* hypervisor yield interface */

That name also sucks chunks, yield isn't a lock related term.

> +#define ALTERNATIVE_TICKET_LOCK \

But but but, the alternative isn't a ticket lock..!?
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