linux-kernel - Re: [PATCH 1/2] x86/entry: Avoid interrupt flag save and restore

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Date:	Wed, 01 Jun 2016 10:52:34 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	x86@...nel.org
Cc:	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...nel.org.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/2] x86/entry: Avoid interrupt flag save and restore

On Mon, 2016-05-30 at 14:30 +0200, Paolo Bonzini wrote:
> Thanks to all the work that was done by Andy Lutomirski and others,
> enter_from_user_mode and prepare_exit_to_usermode are now called only
> with
> interrupts disabled.  Let's provide them a version of
> user_enter/user_exit
> that skips saving and restoring the interrupt flag.
> 
> On an AMD-based machine I tested this patch on, with force-enabled
> context tracking, the speed-up in system calls was 90 clock cycles or
> 6%,
> measured with the following simple benchmark:
> 

Reviewed-by: Rik van Riel <riel@...hat.com>

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