linux-kernel - Re: [PATCH 2/4, v2] x86: enlightenment for ticket spin locks

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Message-Id: <4C2B6AD60200007800008D90@vpn.id2.novell.com>
Date:	Wed, 30 Jun 2010 15:03:34 +0100
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"Jeremy Fitzhardinge" <jeremy@...p.org>
Cc:	"mingo@...e.hu" <mingo@...e.hu>,
	"Stefano Stabellini" <stefano.stabellini@...citrix.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"Ky Srinivasan" <KSrinivasan@...ell.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hpa@...or.com" <hpa@...or.com>
Subject: Re: [PATCH 2/4, v2] x86: enlightenment for ticket spin locks -
	 Xen implementation

>>> On 30.06.10 at 15:23, Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> For spinlocks, the pvop calls should only be in the slow case: when a
> spinlock has been spinning for long enough, and on unlock when there's
> someone waiting for the lock.  The fastpath (no contention lock and
> unlock) should have no extra calls.

Then what was all that performance regression noise concerning
pvops spinlocks about, leading to CONFIG_PARAVIRT_SPINLOCKS
being separated from the base CONFIG_PARAVIRT?

Afaics the unlock still involves a function call *in all cases* with
pvops spinlocks, whereas it's a single inline instruction without.

Jan

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