linux-kernel - Re: [PATCH] sched: sync with the 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]

Message-ID: <20150813152212.GE16853@twins.programming.kicks-ass.net>
Date:	Thu, 13 Aug 2015 17:22:12 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	Byungchul Park <byungchul.park@....com>, mingo@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: sync with the cfs_rq when changing sched class

On Thu, Aug 13, 2015 at 10:15:28AM +0800, Yuyang Du wrote:
> On Thu, Aug 13, 2015 at 05:21:27PM +0900, Byungchul Park wrote:
> > 
> > yuyang said that switched_to don't need to consider task's load because it
> > can have meaningless value. but i think considering task's load is better
> > than leaving it unattended at all. and we can also use switched_to if we 
> > consider task's load in switched_to.
> 
> when did I say "don't need to consider..."?
> 
> Doing more does not mean better, or just trivial. BTW, the task switched_to
> does not have to be switched_from before. 

Correct, there's a few corner cases we need to consider.

However, I think we unconditionally call init_entity_runnable_average()
on all tasks, regardless of their 'initial' sched class, so it should
have a valid state.

Another thing to consider is the state being very stale, suppose it
started live as FAIR, ran for a bit, got switched to !FAIR by means of
sys_sched_setscheduler()/sys_sched_setattr() or similar, runs for a long
time and for some reason gets switched back to FAIR, we need to age and
or re-init things.

I _think_ we can use last_update_time for that, but I've not looked too
hard.

That is, age based on last_update_time, if all 0, reinit, or somesuch.

The most common case of switched_from()/switched_to() is Priority
Inheritance, and that typically results in very short lived stints as
!FAIR and the avg data should be still accurate by the time we return.
--
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/