Re: [PATCH 3/3] vhost_net: tx support batching

[Jason Wang]

On 2016å11æ10æ 04:05, Michael S. Tsirkin wrote:
> On Wed, Nov 09, 2016 at 03:38:33PM +0800, Jason Wang wrote:
> > This patch tries to utilize tuntap rx batching by peeking the tx
> > virtqueue during transmission, if there's more available buffers in
> > the virtqueue, set MSG_MORE flag for a hint for tuntap to batch the
> > packets. The maximum number of batched tx packets were specified
> > through a module parameter: tx_bached.
> >
> > When use 16 as tx_batched:
> When using
>
> > Pktgen test shows 16% on tx pps in guest.
> > Netperf test does not show obvious regression.
> Why doesn't netperf benefit?

This is probably because the tests (4VCPU, 1queue, TCP, mlx4) does not 
produce 100% stress on vhost thread. In pktgen test, 100% stress on 
vhost thread is achieved easily.

> > For safety, 1 were used as the default value for tx_batched.
> s/were used/is used/
>
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> These tests unfortunately only run a single flow.
> The concern would be whether this increases latency when
> NIC is busy with other flows, so I think this is what
> you need to test.

Multiple flows were tested too, no obvious improvement/regression were 
found.


> > ---
> >   drivers/vhost/net.c   | 15 ++++++++++++++-
> >   drivers/vhost/vhost.c |  1 +
> >   drivers/vhost/vhost.h |  1 +
> >   3 files changed, 16 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> > index 5dc128a..51c378e 100644
> > --- a/drivers/vhost/net.c
> > +++ b/drivers/vhost/net.c
> > @@ -35,6 +35,10 @@ module_param(experimental_zcopytx, int, 0444);
> >   MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;"
> >   		                       " 1 -Enable; 0 - Disable");
> >   
> > +static int tx_batched = 1;
> > +module_param(tx_batched, int, 0444);
> > +MODULE_PARM_DESC(tx_batched, "Number of patches batched in TX");
> > +
> >   /* Max number of bytes transferred before requeueing the job.
> >    * Using this limit prevents one virtqueue from starving others. */
> >   #define VHOST_NET_WEIGHT 0x80000
> I think we should do some tests and find a good default.

Ok, will test 4 and 32 to see if there's any difference. (Btw, 16 were 
chosed since dpdk tends to batch 16 packet during TX).

Thanks