[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Wed, 6 Jun 2018 14:29:57 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Andrea Parri <andrea.parri@...rulasolutions.com>
Cc: Viresh Kumar <viresh.kumar@...aro.org>,
Daniel Lezcano <daniel.lezcano@...aro.org>, rjw@...ysocki.net,
linux-kernel@...r.kernel.org,
Eduardo Valentin <edubezval@...il.com>,
Javi Merino <javi.merino@...nel.org>,
Leo Yan <leo.yan@...aro.org>,
Kevin Wangtao <kevin.wangtao@...aro.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
Rui Zhang <rui.zhang@...el.com>,
Daniel Thompson <daniel.thompson@...aro.org>,
"open list:POWER MANAGEMENT CORE" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH V5] powercap/drivers/idle_injection: Add an idle
injection framework
On Wed, Jun 06, 2018 at 02:05:39PM +0200, Andrea Parri wrote:
> Hi Daniel, Viresh,
>
> On Wed, Jun 06, 2018 at 04:15:28PM +0530, Viresh Kumar wrote:
> > On 06-06-18, 12:22, Daniel Lezcano wrote:
> > > (mb() are done in the atomic operations AFAICT).
>
> To do my bit, not all atomic ops do/imply memory barriers; e.g.,
>
> [from Documentation/atomic_t.txt]
>
> - non-RMW operations [e.g., atomic_set()] are unordered
>
> - RMW operations that have no return value [e.g., atomic_inc()] are unordered
Quite so indeed.
> > AFAIU, it is required to make sure the operations are seen in a particular order
> > on another CPU and the compiler doesn't reorganize code to optimize it.
> >
> > For example, in our case what if the compiler reorganizes the atomic-set
> > operation after wakeup-process ? But maybe that wouldn't happen across function
> > calls and we should be safe then.
>
> IIUC, wake_up_process() implies a full memory barrier and a compiler barrier,
> due to:
Yes, the wakeup being a RELEASE (at least) is a fairly fundamental
property for causality. You expect the woken task to observe the
condition it got woken up on.
Powered by blists - more mailing lists