linux-kernel - Re: [PATCH RFC 0/4] vsock/virtio: optimizations to increase the throughput

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Date:   Thu, 4 Apr 2019 14:04:10 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     netdev@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH RFC 0/4] vsock/virtio: optimizations to increase the
 throughput

On Thu, Apr 04, 2019 at 06:47:15PM +0200, Stefano Garzarella wrote:
> On Thu, Apr 04, 2019 at 11:52:46AM -0400, Michael S. Tsirkin wrote:
> > I simply love it that you have analysed the individual impact of
> > each patch! Great job!
> 
> Thanks! I followed Stefan's suggestions!
> 
> > 
> > For comparison's sake, it could be IMHO benefitial to add a column
> > with virtio-net+vhost-net performance.
> > 
> > This will both give us an idea about whether the vsock layer introduces
> > inefficiencies, and whether the virtio-net idea has merit.
> > 
> 
> Sure, I already did TCP tests on virtio-net + vhost, starting qemu in
> this way:
>   $ qemu-system-x86_64 ... \
>       -netdev tap,id=net0,vhost=on,ifname=tap0,script=no,downscript=no \
>       -device virtio-net-pci,netdev=net0
> 
> I did also a test using TCP_NODELAY, just to be fair, because VSOCK
> doesn't implement something like this.

Why not?

> In both cases I set the MTU to the maximum allowed (65520).
> 
>                         VSOCK                        TCP + virtio-net + vhost
>                   host -> guest [Gbps]                 host -> guest [Gbps]
> pkt_size  before opt. patch 1 patches 2+3 patch 4     TCP_NODELAY
>   64          0.060     0.102     0.102     0.096         0.16        0.15
>   256         0.22      0.40      0.40      0.36          0.32        0.57
>   512         0.42      0.82      0.85      0.74          1.2         1.2
>   1K          0.7       1.6       1.6       1.5           2.1         2.1
>   2K          1.5       3.0       3.1       2.9           3.5         3.4
>   4K          2.5       5.2       5.3       5.3           5.5         5.3
>   8K          3.9       8.4       8.6       8.8           8.0         7.9
>   16K         6.6      11.1      11.3      12.8           9.8        10.2
>   32K         9.9      15.8      15.8      18.1          11.8        10.7
>   64K        13.5      17.4      17.7      21.4          11.4        11.3
>   128K       17.9      19.0      19.0      23.6          11.2        11.0
>   256K       18.0      19.4      19.8      24.4          11.1        11.0
>   512K       18.4      19.6      20.1      25.3          10.1        10.7
> 
> For small packet size (< 4K) I think we should implement some kind of
> batching/merging, that could be for free if we use virtio-net as a transport.
> 
> Note: Maybe I have something miss configured because TCP on virtio-net
> for host -> guest case doesn't exceed 11 Gbps.
> 
>                         VSOCK                        TCP + virtio-net + vhost
>                   guest -> host [Gbps]                 guest -> host [Gbps]
> pkt_size  before opt. patch 1 patches 2+3             TCP_NODELAY
>   64          0.088     0.100     0.101                   0.24        0.24
>   256         0.35      0.36      0.41                    0.36        1.03
>   512         0.70      0.74      0.73                    0.69        1.6
>   1K          1.1       1.3       1.3                     1.1         3.0
>   2K          2.4       2.4       2.6                     2.1         5.5
>   4K          4.3       4.3       4.5                     3.8         8.8
>   8K          7.3       7.4       7.6                     6.6        20.0
>   16K         9.2       9.6      11.1                    12.3        29.4
>   32K         8.3       8.9      18.1                    19.3        28.2
>   64K         8.3       8.9      25.4                    20.6        28.7
>   128K        7.2       8.7      26.7                    23.1        27.9
>   256K        7.7       8.4      24.9                    28.5        29.4
>   512K        7.7       8.5      25.0                    28.3        29.3
> 
> For guest -> host I think is important the TCP_NODELAY test, because TCP
> buffering increases a lot the throughput.
> 
> > One other comment: it makes sense to test with disabling smap
> > mitigations (boot host and guest with nosmap).  No problem with also
> > testing the default smap path, but I think you will discover that the
> > performance impact of smap hardening being enabled is often severe for
> > such benchmarks.
> 
> Thanks for this valuable suggestion, I'll redo all the tests with nosmap!
> 
> Cheers,
> Stefano