linux-kernel - Re: kmap_atomic and preemption

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Message-ID: <20160504155345.5fdd366e@free-electrons.com>
Date:	Wed, 4 May 2016 15:53:45 +0200
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <dahi@...ux.vnet.ibm.com>,
	Russell King <linux@....linux.org.uk>,
	lkml <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: kmap_atomic and preemption

Hello,

On Wed, 4 May 2016 15:47:29 +0200, Peter Zijlstra wrote:

> static inline void *kmap_atomic(struct page *page)
> {
> 	preempt_disable();
> 	pagefault_disable();
> 	if (!PageHighMem(page))
> 		return page_address(page);
> 
> 	return __kmap_atomic(page);
> }

This is essentially what has been done on ARM in commit
9ff0bb5ba60638a688a46e93df8c5009896672eb, showing a pretty significant
improvement in network workloads.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com