linux-kernel - Re: [PATCH v2 3/3] X86: Add a thread cpu time implementation to vDSO

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Date:	Fri, 02 Jan 2015 08:31:33 -0700
From:	David Ahern <dsahern@...il.com>
To:	Shaohua Li <shli@...com>, Peter Zijlstra <peterz@...radead.org>
CC:	Andy Lutomirski <luto@...capital.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Kernel-team@...com,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH v2 3/3] X86: Add a thread cpu time implementation to vDSO

On 1/1/15 7:59 PM, Shaohua Li wrote:
> I'm wondering how we could use the perf to implament a clock_gettime.
> reading the perf fd or using ioctl is slow so reading the mmap
> ringbuffer is the only option. But as far as I know the ringbuffer has
> data only when an event is generated. Between two events, there is
> nothing we can read from the ringbuffer. Then how can application get
> time info in the interval?

Are you wanting to read perf_clock from userspace?

David
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