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

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Date:	Thu, 22 Oct 2015 19:16:02 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Rick Jones <rick.jones2@....com>
Cc:	Jason Wang <jasowang@...hat.com>, 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 Thu, Oct 22, 2015 at 08:46:33AM -0700, Rick Jones wrote:
> 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

Absolutely, merging a new kernel API just for a specific
benchmark doesn't make sense.
I'm guessing this is just an early RFC, a fuller submission
will probably include more numbers.

-- 
MST
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