linux-kernel - Re: [PATCH v4 0/5] getcpu

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Message-ID: <56CD091A.4060009@zytor.com>
Date:	Tue, 23 Feb 2016 17:36:26 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	Paul Turner <pjt@...gle.com>, Andrew Hunter <ahh@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...capital.net>,
	Andi Kleen <andi@...stfloor.org>,
	Dave Watson <davejwatson@...com>, Chris Lameter <cl@...ux.com>,
	Ben Maurer <bmaurer@...com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH v4 0/5] getcpu_cache system call for 4.6

On 02/23/2016 03:28 PM, Mathieu Desnoyers wrote:
> Hi,
> 
> Here is a patchset implementing a cache for the CPU number of the
> currently running thread in user-space.
> 
> Benchmarks comparing this approach to a getcpu based on system call on
> ARM show a 44x speedup. They show a 14x speedup on x86-64 compared to
> executing lsl from a vDSO through glibc.
> 
> I'm added a man page in the changelog of patch 1/3, which shows an
> example usage of this new system call.
> 
> This series is based on v4.5-rc5, submitted for Linux 4.6.
> 
> Feedback is welcome,
> 

What is the resulting context switch overhead?

	-hpa