linux-kernel - Re: [patch] CFS scheduler, -v7

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: <200705031142.02550.a1426z@gawab.com>
Date:	Thu, 3 May 2007 11:42:02 +0300
From:	Al Boldi <a1426z@...ab.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [patch] CFS scheduler, -v7

Ingo Molnar wrote:
> * Al Boldi <a1426z@...ab.com> wrote:
> > > i'm pleased to announce release -v7 of the CFS scheduler patchset.
> > > (The main goal of CFS is to implement "desktop scheduling" with as
> > > high quality as technically possible.)
> > >
> > >
> > > As usual, any sort of feedback, bugreport, fix and suggestion is
> > > more than welcome,
> >
> > This one seems on par with SD, [...]
>
> excellent :-)
>
> > [...] but there are still some nice issues.
> >
> > Try running 3 chew.c's, then renicing one to -10, starves others for
> > some seconds while switching prio-level.  Now renice it back to 10, it
> > starves for up to 45sec.
>
> ok - to make sure i understood you correctly: does this starvation only
> occur right when you renice it (when switching prio levels),

Yes.

> and it gets
> rectified quickly once they get over a few reschedules?

Well, depending on nice level this delay may be more than 45sec.

And, in cfs-v8 there is an additional repeating latency blip akin to an 
expiry when running procs at different nice levels.  chew.c shows this 
clearly.

> > Also, nice levels are only effective on every other step; ie:
> >  ... -3/-2 , -1/0 , 1/2 ... yields only 20 instead of 40 prio-levels.
>
> yeah - this is a first-approximation thing.
>
> Some background: in the upstream scheduler (and in SD) nice levels are
> linearly scaled, while in CFS they are exponentially scaled. I did this
> because i believe exponential is more logical: regardless of which nice
> level a task uses, if it goes +2 nice levels up then it will halve its
> "fair CPU share". So for example the CPU consumption delta between nice
> 0 and nice +10 is 1/32 - and so is the delta between -5 and +5, -10 and
> -5, etc. This makes nice levels _alot_ more potent than upstream's
> linear approach.

Actually, I think 1/32 for +10 is a bit to strong.  Introducing a scalefactor 
tunable may be useful.

Also, don't you think it reasonable to lower-bound the timeslices?


Thanks!

--
Al

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/