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

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Message-ID: <4C2B57CA.3070807@goop.org>
Date:	Wed, 30 Jun 2010 16:42:18 +0200
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Jan Beulich <JBeulich@...ell.com>
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 06/30/2010 04:36 PM, Jan Beulich wrote:
> Are we perhaps talking about different things? I'm referring to
>
> static __always_inline void arch_spin_unlock(struct arch_spinlock *lock)
> {
> 	PVOP_VCALL1(pv_lock_ops.spin_unlock, lock);
> }
>
> which is an indirect call which, as I understand it, gets replaced
> with a direct one at runtime. But it remains to be a call (as opposed
> to being a single inc instructions without CONFIG_PARAVIRT_SPINLOCKS).
>   

Sorry, I'm referring to pv ticketlocks, not the current
PARAVIRT_SPINLOCKS code.  I agree the current PARAVIRT_SPINLOCKS
implementation is suboptimal and needs to be replaced with something
that's only called on the slow path.  I just think the existing
paravirt_ops mechanism can be used to implement it rather than adding
something new.

    J
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