DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=message-id:date:from:to:subject:cc:in-reply-to:mime-version
         :content-type:content-transfer-encoding:content-disposition
         :references;
        b=t7rfxsa9IEEqWFxOlN+fxDYzmvRZs7j7K/yXb+103P35ec6kcvWWCtB+dnURXiEaNG
         Zxc1gVJAGmYtfAEPsAVi3DikrXo3eE0MveLjEmwQFe6D5onqly+IFSdZj59gpXCkKpuW
         O3rQ1wg5pmM8t6oHsyvReKgERr2/hPy3QOoEY=
Message-ID: <29495f1d0811191411q374ee7eel600766634372385b@mail.gmail.com>
Date: Wed, 19 Nov 2008 14:11:57 -0800
From: "Nish Aravamudan" <nish.aravamudan@gmail.com>
To: "Max Krasnyansky" <maxk@qualcomm.com>
Subject: Re: Using cpusets for configuration/isolation [Was Re: RT sched: cpupri_vec lock contention with def_root_domain and no load balance]
Cc: "Peter Zijlstra" <peterz@infradead.org>,
       "Gregory Haskins" <ghaskins@novell.com>,
       "Dimitri Sivanich" <sivanich@sgi.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "Ingo Molnar" <mingo@elte.hu>
In-Reply-To: <4923A0A8.5050009@qualcomm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
References: <29495f1d0811071123x37d910a8w6c1604b8159954ec@mail.gmail.com>
	 <4923731E.7010601@qualcomm.com>
	 <29495f1d0811181811r1a7476ceyb5cb4a86e11e7651@mail.gmail.com>
	 <4923A0A8.5050009@qualcomm.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 3497
Lines: 67

Max,

On Tue, Nov 18, 2008 at 9:14 PM, Max Krasnyansky <maxk@qualcomm.com> wrote:
> Nish Aravamudan wrote:
>> On Tue, Nov 18, 2008 at 5:59 PM, Max Krasnyansky <maxk@qualcomm.com> wrote:
>>> I do not see how 'partfs' that you described would be different from
>>> 'cpusets' that we have now. Just ignore 'tasks' files in the cpusets and you
>>> already have your 'partfs'. You do _not_ have to use cpuset for assigning
>>> tasks if you do not want to. Just use them to define sets of cpus and keep
>>> all the tasks in the 'root' set. You can then explicitly pin your threads
>>> down with pthread_set_affinity().
>>
>> I guess you're right. It still feels a bit kludgy, but that is probably just me.
>>
>> I have wondered, though, if it makes sense to provide an "isolated"
>> file in /sys/devices/system/cpu/cpuX/ to do most of the offline
>> sequence, break sched_domains and remove a CPU from the load balancer
>> (rather than turning the load balancer off), rather than requiring a
>> user to explicitly do an offline/online.
> I do not see any benefits in exposing a special 'isolated' bit and have it do
> the same thing that the cpu hotplug already does. As I explained in other
> threads cpu hotplug is a _perfect_ fit for the isolation purposes. In order to
> isolate a CPU dynamically (ie at runtime) we need to flush pending work, flush
> chaches, move tasks and timers, etc. Which is _exactly_ what cpu hotplug code
> does when it brings CPU down. There is no point in reimplementing it.

Ok, I guess I was just referring to the intent of the administrator
and making it a bit clearer. But using syspart or even a simple
script, it's easy enough to alias the offline/online sequence.

> btw It sounds like you misunderstood the meaning of the
> cpuset.sched_load_balance flag. It's does not turn really turn load balancer
> off, it simply causes cpus in different cpusets to be put into separate sched
> domains. In other words it already does exactly what you're asking for.

Ok, I'm re-reading the cpusets.txt section. Sorry for my confusion and
thanks for the clarification.

>> I guess it can all be rather
>> transparently masked via a userspace tool, but we don't have a common
>> one yet.
> I do :). It's called 'syspart'
>        http://git.kernel.org/?p=linux/kernel/git/maxk/syspart.git;a=summary
> I'll push an updated version in a couple of days.

Has there been any effort to start driving this into distributions?

>> I do have a question, though: is your recommendation to just turn the
>> load balancer off in the cpuset you create that has the isolated CPUs?
>> I guess the conceptual issue I was having was that the root cpuset (I
>> think) always contains all CPUs and all memory nodes. So even if you
>> put some CPUs in a cpuset under the root one, and isolate them using
>> hotplug + disabling the load balancer in that cpuset, those CPUs are
>> still available to tasks in the root cpuset? Maybe I'm just missing a
>> step in the configuration, but it seems like as long as the global
>> (root cpuset) load balancer is on, a CPU can't be guaranteed to stay
>> isolated?
> Take a look at what 'syspart' does. In short yes, of course we need to set
> sched_load_balance flag in root cpuset to 0.

Will do, thanks,
Nish
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/