linux-kernel - Re: [PATCH 3/4] sched: introduce synchronized idle injection

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: <20151118140440.GB30184@e105550-lin.cambridge.arm.com>
Date:	Wed, 18 Nov 2015 14:04:41 +0000
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Len Brown <len.brown@...el.com>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	Eduardo Valentin <edubezval@...il.com>,
	Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH 3/4] sched: introduce synchronized idle injection

On Wed, Nov 18, 2015 at 01:49:46PM +0100, Peter Zijlstra wrote:
> On Wed, Nov 18, 2015 at 12:27:04PM +0000, Morten Rasmussen wrote:
> > On Wed, Nov 18, 2015 at 11:35:41AM +0100, Peter Zijlstra wrote:
> > > On Wed, Nov 18, 2015 at 09:36:22AM +0100, Ingo Molnar wrote:
> > > > What will such throttling do to latencies, as observed by user-space tasks? What's 
> > > > the typical expected frequency of the throttling frequency that you are targeting?
> > > 
> > > The default has 5ms (iirc) of forced idle, so depending on what you do,
> > > noticeable to outright painful.
> > 
> > IIUC, it is 5 ticks, not ms.
> 
> The code uses hrtimers (badly), this means there _should_ not be a tick
> dependency.

Then I'm confused :-/

I see the hrtimers, but the actual idle duration appears to be in ticks
rather than ms and then converted later.

+/* Duration of idle time in ticks of each injection period */                                                                               
+unsigned int sysctl_sched_cfs_idle_inject_duration = 5UL;

...and futher down we have:

+       duration_msec = jiffies_to_msecs(sysctl_sched_cfs_idle_inject_duration);

I will go back and look harder.

> 
> > Which raises the question, doesn't that mean that we get disturbed four
> > times on each cpu during the forced idle period? So idle injection only
> > makes sense if the platform has package states with a target residency
> > less than a jiffy. Or, do we enter NOHZ idle? I haven't looked closely
> > enough to figure out yet.
> 
> The idea is to hit NOHZ.

Nice!
--
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/