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

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Message-ID: <20141024220423.GB10501@worktop.programming.kicks-ass.net>
Date:	Sat, 25 Oct 2014 00:04:23 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Waiman Long <waiman.long@...com>
Cc:	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 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 only really care about bare metal.
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