linux-kernel - Re: [PATCH] Extend mwait idle to optimize away CAL and RES interrupts to an idle CPU -v1

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:	Mon, 27 Feb 2012 09:45:54 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Venki Pallipadi <venki@...gle.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Aaron Durbin <adurbin@...gle.com>,
	Paul Turner <pjt@...gle.com>,
	Yong Zhang <yong.zhang0@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Extend mwait idle to optimize away CAL and RES
 interrupts to an idle CPU -v1

On Thu, 2012-02-23 at 11:34 -0800, Venki Pallipadi wrote:

> > > +             local_bh_disable();
> > > +             local_irq_disable();
> >
> > That local_bh_disable() is completely superfluous, disabling IRQs
> > already kills bh.
> 
> The reason for local_bh_disable/enable was to check for potential
> softirqs after these interrupt.

Why is that needed? We never wrap local_irq_disable() in bh muck?


> > Why doesn't ipiless_idle_exit() call this? That would keep it isolated
> > to just those idle routines that actually use mwait instead of bothering
> > the generic idle paths with this.
> 
> ipiless_idle_exit is called in the inner most part of idle entry exit.
> In mwait case we may not even have interrupts enabled at that time and
> there is code that does idle residency timing etc which will get
> impacted if we start doing the pending ipi work there. Doing it at
> higher level along with things like enter-exit tickless felt nicer.

But but but, an actual interrupt can be handled before the instruction
after mwait, so why would this be a problem?

--
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/