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Subject: Re: [PATCH v4 0/5] getcpu_cache system call for 4.6
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Russell King <linux@arm.linux.org.uk>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>
References: <1456270120-7560-1-git-send-email-mathieu.desnoyers@efficios.com>
Cc: linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        Paul Turner <pjt@google.com>, Andrew Hunter <ahh@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Andi Kleen <andi@firstfloor.org>, Dave Watson <davejwatson@fb.com>,
        Chris Lameter <cl@linux.com>, Ben Maurer <bmaurer@fb.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Josh Triplett <josh@joshtriplett.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>
From: "H. Peter Anvin" <hpa@zytor.com>
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Date: Tue, 23 Feb 2016 17:36:26 -0800
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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