On Thu, 2011-03-17 at 08:18 -0700, Shirley Ma wrote:
> On Thu, 2011-03-17 at 07:02 +0200, Michael S. Tsirkin wrote:
> > So, this just tries to make sure there's enough space for
> > max packet in the ring, if not - drop and return OK.
> > Why bother checking beforehand though?
> > If that's what we want to do, we can just call add_buf and see
> > if it fails?
>
> In add_buf, there is an additional kick, see below. I added check
> capacity to avoid this, thought it would be better performance. I will
> retest it w/i add_buf to see the performance difference.
>
> if (vq->num_free < out + in) {
> pr_debug("Can't add buf len %i - avail = %i\n",
> out + in, vq->num_free);
> /* FIXME: for historical reasons, we force a notify
> here
> if
> * there are outgoing parts to the buffer. Presumably
> the
> * host should service the ring ASAP. */
> if (out)
> vq->notify(&vq->vq);
> END_USE(vq);
> return -ENOSPC;
> }
>
More test results:
UDP_STREAM test results (% is guest vcpu, guest has 2 vpus):
Send(netperf)
----
size 2.6.38-rc8 2.6.38-rc8+ 2.6.38-rc8
addbuf failure check capacity
-----------------------------------------------------
1K 1541.0/50.14% 2169.1/50.03% 3018.9/50%
2K 1649.7/33.74% 3362.6/50.18% 4518.8/50.47%
4K 2957.8/44.83% 5965.9/50.03% 9592.5/50%
8K 3788/39.01% 9852.8/50.25% 15483.8/50%
16K 4736.1/34.13% 14946.5/50.01% 21645.0/50%
Recv(netserver w/i recv errors)
----
1K 1541/8.36% 1554.4/9.67% 1675.1/11.26%
2K 1649.7/33.4% 1945.5/5.59% 2160.6/5.99%
4K 2556.3/5.07% 3044.8/7.12% 3118.9/7.86%
8K 3775/39.01% 4361/9/9.14% 4017.1/7.89%
16K 4466.4/8.56% 4435.2/10.95% 4446.8/9.92%
TCP_STREAM test results (% is guest vcpu, guest has two vcpus):
size 2.6.38-rc8 2.6.38-rc8+ 2.6.38-rc8
addbuf failure check capacity
------------------------------------------------------
1K 2381.10/42.49% 5686.01/50.08% 5599.15/50.42%
2K 3205.08/49.18% 8675.93/48.59% 9241.86/48.42%
4K 5231.24/34.12% 9309.67/42.07% 9321.87/40.94%
8K 7952.74/35.85% 9001.95/38.26% 9265.45/37.63%
16K 8260.68/35.07% 7911.52/34.35% 8310.29/34.28%
64K 9103.75/28.98% 9219.12/31.52% 9094.38/29.44%
qemu-kvm host cpu utilization also saved for both addbuf failure and
check capacity patches, vhost cpu utilization are similar in all case.
Looks like the additional guest notify in add_buf doesn't cost that much
than I thought to be.
Thanks
Shirley
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