linux-kernel - Re: [PATCH RFC] remove jump_label optimization for perf sched events

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: <1321537668.27735.38.camel@twins>
Date:	Thu, 17 Nov 2011 14:47:48 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Avi Kivity <avi@...hat.com>
Cc:	Gleb Natapov <gleb@...hat.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, Jason Baron <jbaron@...hat.com>,
	rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH RFC] remove jump_label optimization for perf sched events

On Thu, 2011-11-17 at 15:24 +0200, Avi Kivity wrote:
> On 11/17/2011 03:10 PM, Peter Zijlstra wrote:
> > On Thu, 2011-11-17 at 15:00 +0200, Gleb Natapov wrote:
> >
> > > > That said, I'd much rather throttle this particular jump label than
> > > > remove it altogether, some people really don't like all this scheduler
> > > > hot path crap.
> > > What about moving perf_event_task_sched() to sched_(in|out)_preempt_notifiers?
> > > preempt notifiers checking is already on the scheduler hot path, so no
> > > additional overhead for perf case.
> >
> > Same problem really, some people complain about the overhead of preempt
> > notifiers, also not all kernels have those in. 
> 
> We could combine the two, sort-circuit preempt notifiers with jump
> labels if empty && not much activity on them.

Jump-labels are still more efficient, also I don't much like preempt
notifiers.

> > Futhermore I loathe notifier lists because they obscure wtf is done.
> 
> That's life in a general purpose kernel, if everyone gets their hook in
> to keep their code clean, the scheduler will bloat.

Uhm, no. The bloat isn't different, the only difference is you can
actually see it. So I very much prefer direct hooks.

> An advantage of preempt notifiers is that you can make the perf code
> modular.

Yeah, and you know I loathe modules even more.
--
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/