Subject: Re: [PATCH v4 6/7] sched: add function nr_running_cpu to expose
 number of tasks running on cpu
From: Tim Chen <tim.c.chen@linux.intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "David S.Miller" <davem@davemloft.net>, Ingo Molnar <mingo@kernel.org>,
        Chandramouli Narayanan <mouli@linux.intel.com>,
        Vinodh Gopal <vinodh.gopal@intel.com>,
        James Guilford <james.guilford@intel.com>,
        Wajdi Feghali <wajdi.k.feghali@intel.com>,
        Jussi Kivilinna <jussi.kivilinna@iki.fi>, linux-crypto@vger.kernel.org,
        linux-kernel@vger.kernel.org
In-Reply-To: <alpine.DEB.2.10.1407151452370.24854@nanos>
References: <1405110784.2970.655.camel@schen9-DESK>
	 <20140714101611.GS9918@twins.programming.kicks-ass.net>
	 <1405354214.2970.663.camel@schen9-DESK>
	 <20140714161432.GC9918@twins.programming.kicks-ass.net>
	 <1405357534.2970.701.camel@schen9-DESK>
	 <20140714181738.GI9918@twins.programming.kicks-ass.net>
	 <1405364908.2970.729.camel@schen9-DESK>
	 <20140714191504.GO9918@twins.programming.kicks-ass.net>
	 <1405367450.2970.750.camel@schen9-DESK>
	 <20140715095045.GV9918@twins.programming.kicks-ass.net>
	 <20140715120728.GR3588@twins.programming.kicks-ass.net>
	 <alpine.DEB.2.10.1407151452370.24854@nanos>
Content-Type: text/plain; charset="UTF-8"
Date: Tue, 15 Jul 2014 11:41:05 -0700
Message-ID: <1405449665.2970.798.camel@schen9-DESK>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org

On Tue, 2014-07-15 at 14:59 +0200, Thomas Gleixner wrote:
> On Tue, 15 Jul 2014, Peter Zijlstra wrote:
> 
> > On Tue, Jul 15, 2014 at 11:50:45AM +0200, Peter Zijlstra wrote:
> > > So you already have an idle notifier (which is x86 only, we should fix
> > > that I suppose), and you then double check there really isn't anything
> > > else running.
> > 
> > Note that we've already done a large part of the expense of going idle
> > by the time we call that idle notifier -- in specific, we've
> > reprogrammed the clock to stop the tick.
> > 
> > Its really wasteful to then generate work again, which means we have to
> > again reprogram the clock etc.
> 
> Doing anything which is not related to idle itself in the idle
> notifier is just plain wrong.

I don't like the kicking the multi-buffer job flush using idle_notifier
path either.  I'll try another version of the patch by doing this in the
multi-buffer job handler path.
 
> 
> If that stuff wants to utilize idle slots, we really need to come up
> with a generic and general solution. Otherwise we'll grow those warts
> all over the architecture space, with slightly different ways of
> wreckaging the world an some more.
> 
> This whole attidute of people thinking that they need their own
> specialized scheduling around the real scheduler is a PITA. All this
> stuff is just damanging any sensible approach of power saving, load
> balancing, etc.
> 
> What we really want is infrastructure, which allows the scheduler to
> actively query the async work situation and based on the results
> actively decide when to process it and where.

I agree with you.  It will be great if we have such infrastructure. 

Thanks.

Tim

--
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/