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

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Date:	Fri, 15 May 2009 09:10:20 +0100
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"Jeremy Fitzhardinge" <jeremy@...p.org>
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

>>> Jeremy Fitzhardinge <jeremy@...p.org> 14.05.09 19:45 >>>
>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?

A patch for the pv-ops kernel would require some time. What I can give you
right away - just for reference - are the sources we currently use in our kernel:
attached.

Jan


Download attachment "spinlock.h" of type "application/octet-stream" (9518 bytes)

Download attachment "spinlock.c" of type "application/octet-stream" (3835 bytes)