linux-kernel - Re: [PATCH 5/5] sched/rt: Optimize find_lowest

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, 27 Jan 2015 17:28:15 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Xunlei Pang <pang.xunlei@...aro.org>, linux-kernel@...r.kernel.org,
	Juri Lelli <juri.lelli@...il.com>
Subject: Re: [PATCH 5/5] sched/rt: Optimize find_lowest_rq() to select a
 cache hot cpu

On Tue, Jan 27, 2015 at 09:56:26AM -0500, Steven Rostedt wrote:
> On Tue, 27 Jan 2015 15:21:36 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Mon, Jan 19, 2015 at 04:49:40AM +0000, Xunlei Pang wrote:
> > > In find_lowest_rq(), if we can't find a wake_affine cpu from
> > > sched_domain, then we can actually determine a cache hot cpu
> > > instead of simply calling "cpumask_any(lowest_mask)" which
> > > always returns the first cpu in the mask.
> > > 
> > > So, we can determine the cache hot cpu during the interation of
> > > sched_domain() in passing.
> > 
> > Steve, I'm not getting this. Why are we using WAKE_AFFINE here?
> > 
> 
> It originated from Gregory Haskins topology patches. See 
>  6e1254d2c41215da27025add8900ed187bca121d

Indeed so; it seems an arbitrary choice.

And the proposed patch seems like a convoluted way to simply remove the
->flags & SD_WAKE_AFFINE test.

Of course, the entire domain loop there assumes a lower domain is
better; yay for SMT being such a good counter example ;-)

Of course, if we remove it here; we should do too for deadline.

--
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/