linux-kernel - Re: [RFC v5 2/9] sched/deadline: improve the tracking of active utilization

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20170327071745.GA10289@e106622-lin>
Date:   Mon, 27 Mar 2017 08:17:45 +0100
From:   Juri Lelli <juri.lelli@....com>
To:     luca abeni <luca.abeni@...tannapisa.it>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Claudio Scordino <claudio@...dence.eu.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [RFC v5 2/9] sched/deadline: improve the tracking of active
 utilization

On 24/03/17 22:47, Luca Abeni wrote:
> Hi Peter,
> 
> On Fri, 24 Mar 2017 14:20:41 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Fri, Mar 24, 2017 at 04:52:55AM +0100, luca abeni wrote:
> > 

[...]

> > 
> > In general I feel it would be nice to have a state diagram included
> > somewhere near these two functions. It would be nice to not have to
> > dig out the PDF every time.
> 
> Ok... Since I am not good at ascii art, would it be ok to add a textual
> description? If yes, I'll add a comment like:
> "
> The utilization of a task is added to the runqueue's active utilization
> when the task becomes active (is enqueued in the runqueue), and is

Is enqueued for the first time on a new period, maybe? It seems to be
contradictory w.r.t. what below (if wakeup before 0 lag time) otherwise.

> removed when the task becomes inactive. A task does not become
> immediately inactive when it blocks, but becomes inactive at the so
> called "0 lag time"; so, we setup the "inactive timer" to fire at the
> "0 lag time". When the "inactive timer" fires, the task utilization is
> removed from the runqueue's active utilization. If the task wakes up
> again on the same runqueue before the "0 lag time", the active
> utilization must not be changed and the "inactive timer" must be
> cancelled. If the task wakes up again on a different runqueue before
> the "0 lag time", then the task's utilization must be removed from the
> previous runqueue's active utilization and must be added to the new
> runqueue's active utilization.
> In order to avoid races between a task waking up on a runqueue while the
> "inactive timer" is running on a different CPU, the "dl_non_contending"
> flag is used to indicate that a task is not on a runqueue but is active
> (so, the flag is set when the task blocks and is cleared when the
> "inactive timer" fires or when the task  wakes up).
> "
> (if this is ok, where can I add this comment?)
> 

Thanks for this Luca. Not sure it adds much to your text above, but we
might want to consider adding something like below?

--->8---
           1st enqueue       +------------------+
                             |                  |
           +---------------->+ ACTIVEcontending |
           |                 |                  |
           |                 +----+------+------+
           |                      |      ^
           |                      |      |
  +--------+-------+              |      |
  |                |     dequeue  |      |  wakeup before
  |    INACTIVE    |              |      |  0 lag time
  |                |              |      |
  +--------+-------+              |      |
           ^                      |      |
           |                      V      |
           |                 +----+------+------+
           |                 |                  |
           +-----------------+ ACTIVEnonCONTEND |
                             |                  |
            0 lag time       +------------------+
            elapsed
--->8---

Thanks,

- Juri