linux-kernel - Re: [PATCH 2/2] show nohz

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Message-ID: <5516D3BC.6030704@redhat.com>
Date:	Sat, 28 Mar 2015 12:15:56 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	LKML <linux-kernel@...r.kernel.org>, Li Zefan <lizefan@...wei.com>,
	Tejun Heo <tj@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 2/2] show nohz_full cpus in sysfs

On 03/28/2015 12:02 PM, Frederic Weisbecker wrote:
> 2015-03-27 22:50 GMT+01:00  <riel@...hat.com>:
>> From: Rik van Riel <riel@...hat.com>
>>
>> Currently there is no way to query which CPUs are in nohz_full
>> mode from userspace.
> 
> Well you can watch dmesg | grep NO_HZ
> But surely sysfs is more convenient from an app.
> 
> I guess it's ok, as long as it's strictly Read Only. Here it seems to
> be the case. And it's not chmod'able, right?

I followed the other code for files in that directory.

Quick testing shows that the cpu info files in
/sys/devices/system/cpu are chmoddable, but writing
to them fails with -EIO because there is no function
set up to handle writes. So yeah, read only :)

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