linux-kernel - Re: [PATCH v12 09/11] pvqspinlock, x86: Add para-virtualization support

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Date:	Sat, 25 Oct 2014 06:30:24 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Waiman Long <waiman.long@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-arch@...r.kernel.org,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	xen-devel@...ts.xenproject.org, kvm@...r.kernel.org,
	Paolo Bonzini <paolo.bonzini@...il.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>
Subject: Re: [PATCH v12 09/11] pvqspinlock, x86: Add para-virtualization
 support

On Sat, 2014-10-25 at 00:04 +0200, Peter Zijlstra wrote: 
> On Fri, Oct 24, 2014 at 04:53:27PM -0400, Waiman Long wrote:
> > The additional register pressure may just cause a few more register moves
> > which should be negligible in the overall performance . The additional
> > icache pressure, however, may have some impact on performance. I was trying
> > to balance the performance of the pv and non-pv versions so that we won't
> > penalize the pv code too much for a bit more performance in the non-pv code.
> > Doing it your way will add a lot of function call and register
> > saving/restoring to the pv code.
> 
> If people care about performance they should not be using virt crap :-)

I tried some benching recently.. where did they hide the fastpaths? :)

-Mike

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