netdev - Re: [PATCH net-next RFC 2/2] vhost

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Date:	Thu, 22 Oct 2015 08:46:33 -0700
From:	Rick Jones <rick.jones2@....com>
To:	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>
Cc:	kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next RFC 2/2] vhost_net: basic polling support

On 10/22/2015 02:33 AM, Michael S. Tsirkin wrote:
> On Thu, Oct 22, 2015 at 01:27:29AM -0400, Jason Wang wrote:
>> This patch tries to poll for new added tx buffer for a while at the
>> end of tx processing. The maximum time spent on polling were limited
>> through a module parameter. To avoid block rx, the loop will end it
>> there's new other works queued on vhost so in fact socket receive
>> queue is also be polled.
>>
>> busyloop_timeout = 50 gives us following improvement on TCP_RR test:
>>
>> size/session/+thu%/+normalize%
>>      1/     1/   +5%/  -20%
>>      1/    50/  +17%/   +3%
>
> Is there a measureable increase in cpu utilization
> with busyloop_timeout = 0?

And since a netperf TCP_RR test is involved, be careful about what 
netperf reports for CPU util if that increase isn't in the context of 
the guest OS.

For completeness, looking at the effect on TCP_STREAM and TCP_MAERTS, 
aggregate _RR and even aggregate _RR/packets per second for many VMs on 
the same system would be in order.

happy benchmarking,

rick jones

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