linux-kernel - Re: deadlock in scheduler enabling HRTICK feature

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: <20130627105303.GD27378@dyad.programming.kicks-ass.net>
Date:	Thu, 27 Jun 2013 12:53:03 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Ahern <dsahern@...il.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, tglx@...utronix.de
Subject: Re: deadlock in scheduler enabling HRTICK feature

On Thu, Jun 27, 2013 at 12:43:09PM +0200, Peter Zijlstra wrote:
> On Wed, Jun 26, 2013 at 10:46:33AM -0600, David Ahern wrote:
> > On 6/26/13 1:05 AM, Peter Zijlstra wrote:
> > >>What is the expectation that the feature provides? not a whole lot of
> > >>documentation on it. I walked down the path wondering if it solved an odd
> > >>problem we are seeing with the CFS in 2.6.27 kernel.
> > >
> > >Its supposed to use hrtimers for slice expiry instead of the regular tick.
> > 
> > So theoretically CPU bound tasks would get preempted sooner? That was my
> > guess/hope anyways.
> 
> Doth the below worketh?
> 

Related to all this; the reason its not enabled by default is that mucking
about with hrtimers all the while is god awful expensive.

I've had ideas about making this a special purpose 'hard-coded' timer in the
hrtimer guts that's only ever re-programmed when the new value is sooner.

By making it a 'special' timer we can avoid the whole rb-tree song and dance;
and by taking 'spurious' short interrupts we can avoid prodding the hardware
too often.

Then again; Thomas will likely throw frozen seafood my way for even proposing
stuff like this and I'm not even sure that's going to be enough to make the
cost acceptable.
--
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/