linux-kernel - Re: Regarding USER_HZ and the exposure of kernel jiffies in userspace

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Message-ID: <alpine.DEB.2.11.1508221626340.3873@nanos>
Date:	Sat, 22 Aug 2015 16:29:27 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	William Breathitt Gray <vilhelm.gray@...il.com>
cc:	linux-kernel@...r.kernel.org, john.stultz@...aro.org
Subject: Re: Regarding USER_HZ and the exposure of kernel jiffies in
 userspace

On Sat, 22 Aug 2015, William Breathitt Gray wrote:
> I believe the error in my understanding is the assumption that _all_
> instances of kernel jiffies exposure in userspace should be scaled; but
> it appears that not all instances are. When are kernel jiffies meant to
> be scaled via USER_HZ, and when are they not?

All instances which are de facto APIs, syscalls and also various files
in proc/ must be in USER_HZ because userspace applications depend on
the USER_HZ value.

proc/timer_list is exempt from that because its more a debugging
interface which is not part of the strict kernel API. And we really
want to see the real values and not the scaled USER_HZ ones for that
purpose. I hope that answers your question.

Thanks,

	tglx

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