linux-kernel - Re: [PATCH] cpufreq: powernv: Export frequency throttle state of the chip through sysfs

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Date:	Thu, 27 Aug 2015 15:47:04 +0530
From:	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
To:	Michael Ellerman <mpe@...erman.id.au>
CC:	rjw@...ysocki.net, stewart@...ux.vnet.ibm.com,
	linux-pm@...r.kernel.org, viresh.kumar@...aro.org,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org
Subject: Re: [PATCH] cpufreq: powernv: Export frequency throttle state of
 the chip through sysfs



On 08/27/2015 03:01 PM, Michael Ellerman wrote:
> On Thu, 2015-08-27 at 14:43 +0530, Shilpasri G Bhat wrote:
>> Create a sysfs 'throttle' attribute per-chip(per-numa-node) to reflect
>> the throttle state of the chip. The usersapce programs can poll on
>> this attribute to keep an eye on the throttle state. Currently we
>> print a log message to notify the user of throttling event. The
>> performance-sensitive applications can monitor the throttle state
>> using this attribute.
> 
> Performance sensitive applications can *poll* on a sysfs file, which does a
> loop over all chips and potentially spams the console with pr_crit() messages ?
> 
> That does not sound like a recipe for success.

Okay.

> 
> What problem are we actually trying to solve here?

How to export the throttle information to the user space, such that it is
consumable by the applications (for example to discard the benchmark run if the
frequency was throttled)?

We already print the throttle information to console. Can we extend this to
notify/broadcast as an event to the applications?

Thanks and Regards,
Shilpa

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