linux-kernel - Re: [PATCH 05/16] sched: SCHED_DEADLINE policy implementation.

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: <4F955B02.7040304@gmail.com>
Date:	Mon, 23 Apr 2012 15:37:06 +0200
From:	Juri Lelli <juri.lelli@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	tglx@...utronix.de, mingo@...hat.com, rostedt@...dmis.org,
	cfriesen@...tel.com, oleg@...hat.com, fweisbec@...il.com,
	darren@...art.com, johan.eker@...csson.com, p.faure@...tech.ch,
	linux-kernel@...r.kernel.org, claudio@...dence.eu.com,
	michael@...rulasolutions.com, fchecconi@...il.com,
	tommaso.cucinotta@...up.it, nicola.manica@...i.unitn.it,
	luca.abeni@...tn.it, dhaval.giani@...il.com, hgu1972@...il.com,
	paulmck@...ux.vnet.ibm.com, raistlin@...ux.it,
	insop.song@...csson.com, liming.wang@...driver.com
Subject: Re: [PATCH 05/16] sched: SCHED_DEADLINE policy implementation.

On 04/23/2012 02:22 PM, Peter Zijlstra wrote:
> On Mon, 2012-04-23 at 14:13 +0200, Juri Lelli wrote:
>> On 04/23/2012 01:32 PM, Peter Zijlstra wrote:
>>> On Fri, 2012-04-06 at 09:14 +0200, Juri Lelli wrote:
>>>> +       /*
>>>> +        * We Keep moving the deadline away until we get some
>>>> +        * available runtime for the entity. This ensures correct
>>>> +        * handling of situations where the runtime overrun is
>>>> +        * arbitrary large.
>>>> +        */
>>>> +       while (dl_se->runtime<= 0) {
>>>> +               dl_se->deadline += dl_se->dl_deadline;
>>>> +               dl_se->runtime += dl_se->dl_runtime;
>>>> +       }
>>>
>>> Does gcc 'optimize' that into a division? If so, it might need special
>>> glue to make it not do that.
>>
>> I got two adds and a jle, no div here..
>
> Gcc is known to change such loops to something like:
>
>   if (runtime<= 0) {
>     tmp = 1 - runtime / dl_runtime;
>     deadline += tmp * dl_deadline;
>     runtime += tmp * dl_runtime;
>   }
>
>

This is what I got for that snippet:

ffffffff81062826 <enqueue_task_dl>:
[...]
ffffffff81062885:       49 03 44 24 20          add    0x20(%r12),%rax
ffffffff8106288a:       49 8b 54 24 28          mov    0x28(%r12),%rdx
ffffffff8106288f:       49 01 54 24 38          add    %rdx,0x38(%r12)
ffffffff81062894:       49 89 44 24 30          mov    %rax,0x30(%r12)
ffffffff81062899:       49 8b 44 24 30          mov    0x30(%r12),%rax
ffffffff8106289e:       48 85 c0                test   %rax,%rax
ffffffff810628a1:       7e e2                   jle    ffffffff81062885 <enqueue_task_dl+0x5f>

So it seems we are fine in this case, right?
It is anyway better to enforce this Gcc behaviour, just to be
on the safe side?

Thanks,

- Juri
--
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/