On 03/06/2017 09:46 AM, Yuanhan Liu wrote:
On Wed, Mar 01, 2017 at 08:36:24AM +0100, Maxime Coquelin wrote:
On 02/23/2017 06:49 AM, Yuanhan Liu wrote:
On Wed, Feb 22, 2017 at 10:36:36AM +0100, Maxime Coquelin wrote:
On 02/22/2017 02:37 AM, Yuanhan Liu wrote:
On Tue, Feb 21, 2017 at 06:32:43PM +0100, Maxime Coquelin wrote:
This patch aligns the Virtio-net header on a cache-line boundary to
optimize cache utilization, as it puts the Virtio-net header (which
is always accessed) on the same cache line as the packet header.
For example with an application that forwards packets at L2 level,
a single cache-line will be accessed with this patch, instead of
two before.
I'm assuming you were testing pkt size <= (64 - hdr_size)?
No, I tested with 64 bytes packets only.
Oh, my bad, I overlooked it. While you were saying "a single cache
line", I was thinking putting the virtio net hdr and the "whole"
packet data in single cache line, which is not possible for pkt
size 64B.
I run some more tests this morning with different packet sizes,
and also with changing the mbuf size on guest side to have multi-
buffers packets:
+-------+--------+--------+-------------------------+
| Txpkt | Rxmbuf | v17.02 | v17.02 + vnet hdr align |
+-------+--------+--------+-------------------------+
| 64 | 2048 | 11.05 | 11.78 |
| 128 | 2048 | 10.66 | 11.48 |
| 256 | 2048 | 10.47 | 11.21 |
| 512 | 2048 | 10.22 | 10.88 |
| 1024 | 2048 | 7.65 | 7.84 |
| 1500 | 2048 | 6.25 | 6.45 |
| 2000 | 2048 | 5.31 | 5.43 |
| 2048 | 2048 | 5.32 | 4.25 |
| 1500 | 512 | 3.89 | 3.98 |
| 2048 | 512 | 1.96 | 2.02 |
+-------+--------+--------+-------------------------+
Could you share more info, say is it a PVP test? Is mergeable on?
What's the fwd mode?
No, this is not PVP benchmark, I have neither another server nor a packet
generator connected to my Haswell machine back-to-back.
This is simple micro-benchmark, vhost PMD in txonly, Virtio PMD in
rxonly. In this configuration, mergeable is ON and no offload disabled
in QEMU cmdline.
Okay, I see. So the boost, as you have stated, comes from saving two
cache line access to one. Before that, vhost write 2 cache lines,
while the virtio pmd reads 2 cache lines: one for reading the header,
another one for reading the ether header, for updating xstats (there
is no ether access in the fwd mode you tested).
That's why I would be interested in more testing on recent hardware
with PVP benchmark. Is it something that could be run in Intel lab?
I think Yao Lei could help on that? But as stated, I think it may
break the performance for bit packets. And I also won't expect big
boost even for 64B in PVP test, judging that it's only 6% boost in
micro bechmarking.
That would be great.
Note that on SandyBridge, on which I see a drop in perf with
microbenchmark, I get a 4% gain on PVP benchmark. So on recent hardware
that show a gain on microbenchmark, I'm curious of the gain with PVP
bench.
Cheers,
Maxime
