linux-kernel - Re: [PATCH v4 0/5] sched_clock: Optimize and avoid deadlock during read from NMI

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Date:	Thu, 12 Feb 2015 19:49:38 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Daniel Thompson <daniel.thompson@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>
CC:	linux-kernel@...r.kernel.org, patches@...aro.org,
	linaro-kernel@...ts.linaro.org,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v4 0/5] sched_clock: Optimize and avoid deadlock during
 read from NMI

On 02/08/15 04:02, Daniel Thompson wrote:
> This patchset optimizes the generic sched_clock implementation by
> removing branches and significantly reducing the data cache profile. It
> also makes it safe to call sched_clock() from NMI (or FIQ on ARM).
>
> The data cache profile of sched_clock() in the original code is
> somewhere between 2 and 3 (64-byte) cache lines, depending on alignment
> of struct clock_data. After patching, the cache profile for the normal
> case should be a single cacheline.
>
> NMI safety was tested on i.MX6 with perf drowning the system in FIQs and
> using the perf handler to check that sched_clock() returned monotonic
> values. At the same time I forcefully reduced kt_wrap so that
> update_sched_clock() is being called at >1000Hz.
>
> Without the patches the above system is grossly unstable, surviving
> [9K,115K,25K] perf event cycles during three separate runs. With the
> patch I ran for over 9M perf event cycles before getting bored.
>

Looks good to me. For the series:

Reviewed-by: Stephen Boyd <sboyd@...eaurora.org>

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Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

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