linux-kernel - Re: [PATCH] clockevents: avoid unnecessary reprograming of event timer

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: <20090213095506.GE17774@elte.hu>
Date:	Fri, 13 Feb 2009 10:55:06 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Michael Davidson <md@...gle.com>, mbligh@...gle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clockevents: avoid unnecessary reprograming of event
	timer


* Thomas Gleixner <tglx@...utronix.de> wrote:

> On Fri, 13 Feb 2009, Ingo Molnar wrote:
> > > +	if (ktime_equal(dev->next_event, expires))
> > > +		return 0;
> > > +
> > 
> > Hm, given that a good high-res source has nanoseconds resolution,
> > what's the chance of this optimization triggering in practice?
> > Near zero i think - unless we trigger useless reprogramming without
> > having added or removed any new timers - but then we should
> > concentrate on analyzing the reason for that redundant reprogramming.
> > 
> > Does it trigger often for you?
> 
> The only point where this should trigger is when we come out of C2/C3
> and switch the local APIC timer back on. There we reload the
> next_event which was discarded in the hardware before we entered C2/C3
> and switched to the broadcast timer. So this change would prevent the
> rearming of the local APIC after coming out of C2/C3 and probably give
> us some new C-State related headaches.

yes, that was my other thought. Albeit arguably the CE code should
set next_event to -1 or so when suspending, out of caution, right?

	Ingo
--
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/