linux-kernel - Re: [PATCH] sched: Avoid side-effect of tickless idle on update_cpu

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:	Tue, 18 May 2010 17:12:02 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Venkatesh Pallipadi <venki@...gle.com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Ken Chen <kenchen@...gle.com>, Paul Turner <pjt@...gle.com>,
	Nikhil Rao <ncrao@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [PATCH] sched: Avoid side-effect of tickless idle on 
 update_cpu_load (v2)

On Mon, 2010-05-17 at 10:52 -0700, Venkatesh Pallipadi wrote:
> > load_i = ((2^i)-1)/(2^i) * load_i + 1/(2^i) * load_(i-1)
> >
> > not
> >
> > load_i = ((2^i)-1)/(2^i) * load_i + 1/(2^i) * cur_load
> 
> Hmm. I assumed you meant
> load_(i-1) is same as cur_load when you said
> >> >Where load_-1 == current load.
> 
> No? Or did I miss something?

load_(i-1) is only load_-1 when i == 0.

But it seems you're right and I misread the code. update_cpu_load() does
take a copy of this_load for each iteration, initially I thought it used
the load of the last iteration.

> For the updates done every tick, it is
> load = degrade * load + (1-degrade) * cur_load
> For updates done with missed ticks
> load = degrade^(missed-1) * load
> load = degrade * load + (1-degrade) * cur_load
> 
> So, cur_load is only accounted for the last tick, and zero load
> assumed for all the missed ticks. 

Right.
--
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/