netdev - Re: [RFC PATCH 00/17] virtual-bus

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Message-ID: <49D60034.1010508@redhat.com>
Date:	Fri, 03 Apr 2009 15:25:24 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	Gregory Haskins <ghaskins@...ell.com>,
	Rusty Russell <rusty@...tcorp.com.au>, anthony@...emonkey.ws,
	andi@...stfloor.org, linux-kernel@...r.kernel.org, agraf@...e.de,
	pmullaney@...ell.com, pmorreale@...ell.com, netdev@...r.kernel.org,
	kvm@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC PATCH 00/17] virtual-bus

Herbert Xu wrote:
> On Thu, Apr 02, 2009 at 07:54:21PM +0300, Avi Kivity wrote:
>   
>> 3ms latency for ping?
>>
>> (ping will always be scheduled immediately when the reply arrives if I  
>> understand cfs, so guest load won't delay it)
>>     
>
> That only happens if the guest immediately does some CPU-intensive
> computation 3ms and assuming its timeslice lasts that long.
>   

 Note that this happens even if the computation is SCHED_BATCH.

> In any case, the same thing will happen right now if the host or
> some other guest on the same CPU hogs the CPU for 3ms.
>
>   

If the host is overloaded, that's fair.  But millisecond latencies 
without host contention is not a good result.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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