linux-kernel - Re: [PATCH v3 2/7] sched: accumulate per-cfs

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]

Date:	Thu, 14 Oct 2010 02:14:56 -0700
From:	Paul Turner <pjt@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	bharata@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	Dhaval Giani <dhaval.giani@...il.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Herbert Poetzl <herbert@...hfloor.at>,
	Avi Kivity <avi@...hat.com>,
	Chris Friesen <cfriesen@...tel.com>,
	Paul Menage <menage@...gle.com>,
	Mike Waychison <mikew@...gle.com>,
	Nikhil Rao <ncrao@...gle.com>
Subject: Re: [PATCH v3 2/7] sched: accumulate per-cfs_rq cpu usage

On Thu, Oct 14, 2010 at 2:01 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, 2010-10-12 at 13:21 +0530, Bharata B Rao wrote:
>> +static void account_cfs_rq_quota(struct cfs_rq *cfs_rq,
>> +               unsigned long delta_exec)
>> +{
>> +       if (cfs_rq->quota_assigned == RUNTIME_INF)
>> +               return;
>> +
>> +       cfs_rq->quota_used += delta_exec;
>> +
>> +       if (cfs_rq->quota_used < cfs_rq->quota_assigned)
>> +               return;
>> +
>> +       cfs_rq->quota_assigned += tg_request_cfs_quota(cfs_rq->tg);
>> +}
>
> That looks iffy, quota_assigned is only ever incremented and can wrap.

This can't advance at a rate faster than ~vruntime and we can't handle
wrapping there anyway (fortunately it would take something like 35k
years?)

> Why not subtract delta_exec and replenish when <0? That keeps the
> numbers small.
>

Accounting in the opposite direction allows us to catch-up in
subsequent periods when a task exceeds its bandwidth across an
interval where we are not able to immediately throttle it (e.g. costly
syscall without config_prempt).  Since we'll continue to accrue the
execution time in this case it will be effectively pre-charged against
the next slice received.
--
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/