linux-kernel - Re: [PATCH] vhost: Add polling mode

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Date:	Sun, 17 Aug 2014 14:58:09 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Razya Ladelsky <RAZYA@...ibm.com>
Cc:	abel.gordon@...il.com, Alex Glikson <GLIKSON@...ibm.com>,
	David Miller <davem@...emloft.net>,
	Eran Raichstein <ERANRA@...ibm.com>,
	Joel Nider <JOELN@...ibm.com>, kvm@...r.kernel.org,
	kvm-owner@...r.kernel.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	Yossi Kuperman1 <YOSSIKU@...ibm.com>
Subject: Re: [PATCH] vhost: Add polling mode

On Sun, Aug 17, 2014 at 03:35:39PM +0300, Razya Ladelsky wrote:
> > > 
> > > Hi Michael,
> > > 
> > > Sorry for the delay, had some problems with my mailbox, and I realized 
> 
> > > just now that 
> > > my reply wasn't sent.
> > > The vm indeed ALWAYS utilized 100% cpu, whether polling was enabled or 
> 
> > > not.
> > > The vhost thread utilized less than 100% (of the other cpu) when 
> polling 
> > > was disabled.
> > > Enabling polling increased its utilization to 100% (in which case both 
> 
> > > cpus were 100% utilized). 
> > 
> > Hmm this means the testing wasn't successful then, as you said:
> > 
> >    The idea was to get it 100% loaded, so we can see that the polling is
> >    getting it to produce higher throughput.
> > 
> > in fact here you are producing more throughput but spending more power
> > to produce it, which can have any number of explanations besides polling
> > improving the efficiency. For example, increasing system load might
> > disable host power management.
> >
> 
> Hi Michael,
> I re-ran the tests, this time with the  "turbo mode" and  "C-states" 
> features off.
> No Polling:
> 1 VM running netperf (msg size 64B): 1107 Mbits/sec
>  Polling:
> 1 VM running netperf (msg size 64B): 1572 Mbits/sec
> 
> 
> 
> 
> 
> 
> 
> As you can see from the new results, the numbers are lower, 
> but relatively (polling on/off) there's no change.
> Thank you,
> Razya

That was just one example. There many other possibilities.  Either
actually make the systems load all host CPUs equally, or divide
throughput by host CPU.

> 
>  
> 
> 
>  
> > 
> > > > -- 
> > > > MST
> > > > 
> > --
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