Re: Xen on ARM IRQ latency and scheduler overhead

From: Dario Faggioli <dario.faggioli@citrix.com>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: edgar.iglesias@xilinx.com, george.dunlap@eu.citrix.com,
	Julien Grall <julien.grall@arm.com>,
	nd@arm.com, xen-devel@lists.xen.org
Subject: Re: Xen on ARM IRQ latency and scheduler overhead
Date: Sat, 18 Feb 2017 01:47:33 +0100	[thread overview]
Message-ID: <1487378853.6732.106.camel@citrix.com> (raw)
In-Reply-To: <alpine.DEB.2.10.1702171559240.9566@sstabellini-ThinkPad-X260>

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On Fri, 2017-02-17 at 16:02 -0800, Stefano Stabellini wrote:
> On Fri, 17 Feb 2017, Stefano Stabellini wrote:
> > 
> > NODEBUG vwfi=idle credit2 fix cpumasks	4000	2370	
> > 4500	3350
> > NODEBUG vwfi=idle credit1 fix cpumasks	3220	2180	
> > 4500	4320
> 
> Actually those are still the old numbers, sorry! 
>
Yeah, I know, I've done the same sooo many times! :-P

> I didn't update the xen
> binary properly. These are the new numbers:
> 
>         	                    AVG	    MIN	    MAX
> 	    WARM MAX
> vwfi=sleep credit2 fix cpumasks	5910	5800	8520	
> 6180
> vwfi=sleep credit1 fix cpumasks	4900	4810	6910	
> 4980
> vwfi=idle  credit2 fix cpumasks	2800	1560	4550	
> 4200
> vwfi=idle  credit1 fix cpumasks	2800	1610	3420	
> 1770
> 
> The difference between credit2 and credit1 is smaller now. In fact
> it's
> zero, when vwfi=idle. 
>
Ok, cool.

> However, with vwfi=sleep, the larger MAX value is
> a bit worrying.
> 
I still think this may be due to the fact that you never stop Credit1's
tick on ARM, which means that, when on Credit1, the system is a lot
more "alive" (e.g., if we were on x86, I'd have said it'd spend less
time in deep C-states, and things like that).

And yes, I still owe you a patch for disabling it.
I'm working on that one. :-)

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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