linux-kernel - Re: [Xen-devel] Performance overhead of paravirt

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Message-ID: <4A0C58BB.3090303@goop.org>
Date:	Thu, 14 May 2009 10:45:31 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Jan Beulich <JBeulich@...ell.com>
CC:	Ingo Molnar <mingo@...e.hu>, Jun Nakajima <jun.nakajima@...el.com>,
	Xiaohui Xin <xiaohui.xin@...el.com>, Xin Li <xin.li@...el.com>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [Xen-devel] Performance overhead of paravirt_ops on	 nativeidentified

Jan Beulich wrote:
> Wouldn't a third solution be to use ticket spinlocks everywhere, i.e. eliminate
> the current indirection, and replace it by an indirection for just the contention
> case? As I view it, the problem for Xen aren't really the ticket locks by
> themselves, but rather the extra spinning involved, which is of concern only
> if a lock is contended. We're using ticket locks quite happily in our kernels,
> with directed instead of global wakeup from the unlock path.
Do you have a patch to illustrate what you mean?  How do you keep track 
of the target vcpu for the directed wakeup?  Are you using the 
event-poll mechanism to block?

    J
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