linux-kernel - Re: [RFC PATCH 3/3] idle: store the idle state index in the struct rq

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: <20140212151626.GE28661@e102568-lin.cambridge.arm.com>
Date:	Wed, 12 Feb 2014 15:16:26 +0000
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Len Brown <len.brown@...el.com>,
	Preeti Murthy <preeti.lkml@...il.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>
Subject: Re: [RFC PATCH 3/3] idle: store the idle state index in the struct rq

On Mon, Feb 03, 2014 at 04:17:47PM +0000, Arjan van de Ven wrote:

[...]

> >> 1) A latency driven one
> >> 2) A performance impact on
> >>
> >> first one is pretty much the exit latency related time, sort of a
> >> "expected time to first instruction" (currently menuidle has the
> >> 99.999% worst case number, which is not useful for this, but is a
> >> first approximation). This is obviously the dominating number for
> >> expected-short running tasks
> >>
> >> second on is more of a "is there any cache/TLB left or is it flushed"
> >> kind of metric. It's more tricky to compute, since what is the cost of
> >> an empty cache (or even a cache migration) after all....  .... but I
> >> suspect it's in part what the scheduler will care about more for
> >> expected-long  running tasks.
> >
> > Yeah, so currently we 'assume' cache hotness based on runtime; see
> > task_hot(). A hint that the CPU wiped its caches might help there.
> 
> if there's a simple api like
> 
> sched_cpu_cache_wiped(int llc)
> 
> that would be very nice for this; the menuidle side knows this
> for some cases and thus can just call it. This would be a very
> small and minimal change

What do you mean by "menuidle side knows this for some cases" ?
You mean you know that some C-state entries imply llc clean/invalidate ?

Thanks,
Lorenzo

--
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/