Subject: Re: [v3 RFC PATCH 0/4] Implement multiqueue virtio-net

From: "Michael S. Tsirkin" <[email-masked]>
Date: Mon, 25 Oct 2010 18:17:18 +0200

On Mon, Oct 25, 2010 at 09:20:38PM +0530, Krishna Kumar2 wrote:
> > Krishna Kumar2/India/IBM@IBMIN wrote on 10/20/2010 02:24:52 PM:
> 
> Any feedback, comments, objections, issues or bugs about the
> patches? Please let me know if something needs to be done.

I am trying to wrap my head around kernel/user interface here.
E.g., will we need another incompatible change when we add multiple RX
queues? Also need to think about how robust our single stream heuristic is,
e.g. what are the chances it will misdetect a bidirectional
UDP stream as a single TCP?

> Some more test results:
> _____________________________________________________
>          Host->Guest BW (numtxqs=2)
> #       BW%     CPU%    RCPU%   SD%     RSD%
> _____________________________________________________
> 1       5.53    .31     .67     -5.88   0
> 2       -2.11   -1.01   -2.08   4.34    0
> 4       13.53   10.77   13.87   -1.96   0
> 8       34.22   22.80   30.53   -8.46   -2.50
> 16      30.89   24.06   35.17   -5.20   3.20
> 24      33.22   26.30   43.39   -5.17   7.58
> 32      30.85   27.27   47.74   -.59    15.51
> 40      33.80   27.33   48.00   -7.42   7.59
> 48      45.93   26.33   45.46   -12.24  1.10
> 64      33.51   27.11   45.00   -3.27   10.30
> 80      39.28   29.21   52.33   -4.88   12.17
> 96      32.05   31.01   57.72   -1.02   19.05
> 128     35.66   32.04   60.00   -.66    20.41
> _____________________________________________________
> BW: 23.5%  CPU/RCPU: 28.6%,51.2%  SD/RSD: -2.6%,15.8%
> 
> ____________________________________________________
> Guest->Host 512 byte (numtxqs=2):
> #       BW%     CPU%    RCPU%   SD%     RSD%
> _____________________________________________________
> 1       3.02    -3.84   -4.76   -12.50  -7.69
> 2       52.77   -15.73  -8.66   -45.31  -40.33
> 4       -23.14  13.84   7.50    50.58   40.81
> 8       -21.44  28.08   16.32   63.06   47.43
> 16      33.53   46.50   27.19   7.61    -6.60
> 24      55.77   42.81   30.49   -8.65   -16.48
> 32      52.59   38.92   29.08   -9.18   -15.63
> 40      50.92   36.11   28.92   -10.59  -15.30
> 48      46.63   34.73   28.17   -7.83   -12.32
> 64      45.56   37.12   28.81   -5.05   -10.80
> 80      44.55   36.60   28.45   -4.95   -10.61
> 96      43.02   35.97   28.89   -.11    -5.31
> 128     38.54   33.88   27.19   -4.79   -9.54
> _____________________________________________________
> BW: 34.4%  CPU/RCPU: 35.9%,27.8%  SD/RSD: -4.1%,-9.3%
> 
> 
> Thanks,
> 
> - KK
> 
> 
> 
> > [v3 RFC PATCH 0/4] Implement multiqueue virtio-net
> >
> > Following set of patches implement transmit MQ in virtio-net.  Also
> > included is the user qemu changes.  MQ is disabled by default unless
> > qemu specifies it.
> >
> >                   Changes from rev2:
> >                   ------------------
> > 1. Define (in virtio_net.h) the maximum send txqs; and use in
> >    virtio-net and vhost-net.
> > 2. vi->sq[i] is allocated individually, resulting in cache line
> >    aligned sq[0] to sq[n].  Another option was to define
> >    'send_queue' as:
> >        struct send_queue {
> >                struct virtqueue *svq;
> >                struct scatterlist tx_sg[MAX_SKB_FRAGS + 2];
> >        } ____cacheline_aligned_in_smp;
> >    and to statically allocate 'VIRTIO_MAX_SQ' of those.  I hope
> >    the submitted method is preferable.
> > 3. Changed vhost model such that vhost[0] handles RX and vhost[1-MAX]
> >    handles TX[0-n].
> > 4. Further change TX handling such that vhost[0] handles both RX/TX
> >    for single stream case.
> >
> >                   Enabling MQ on virtio:
> >                   -----------------------
> > When following options are passed to qemu:
> >         - smp > 1
> >         - vhost=on
> >         - mq=on (new option, default:off)
> > then #txqueues = #cpus.  The #txqueues can be changed by using an
> > optional 'numtxqs' option.  e.g. for a smp=4 guest:
> >         vhost=on                   ->   #txqueues = 1
> >         vhost=on,mq=on             ->   #txqueues = 4
> >         vhost=on,mq=on,numtxqs=2   ->   #txqueues = 2
> >         vhost=on,mq=on,numtxqs=8   ->   #txqueues = 8
> >
> >
> >                    Performance (guest -> local host):
> >                    -----------------------------------
> > System configuration:
> >         Host:  8 Intel Xeon, 8 GB memory
> >         Guest: 4 cpus, 2 GB memory
> > Test: Each test case runs for 60 secs, sum over three runs (except
> > when number of netperf sessions is 1, which has 10 runs of 12 secs
> > each).  No tuning (default netperf) other than taskset vhost's to
> > cpus 0-3.  numtxqs=32 gave the best results though the guest had
> > only 4 vcpus (I haven't tried beyond that).
> >
> > ______________ numtxqs=2, vhosts=3  ____________________
> > #sessions  BW%      CPU%    RCPU%    SD%      RSD%
> > ________________________________________________________
> > 1          4.46    -1.96     .19     -12.50   -6.06
> > 2          4.93    -1.16    2.10      0       -2.38
> > 4          46.17    64.77   33.72     19.51   -2.48
> > 8          47.89    70.00   36.23     41.46    13.35
> > 16         48.97    80.44   40.67     21.11   -5.46
> > 24         49.03    78.78   41.22     20.51   -4.78
> > 32         51.11    77.15   42.42     15.81   -6.87
> > 40         51.60    71.65   42.43     9.75    -8.94
> > 48         50.10    69.55   42.85     11.80   -5.81
> > 64         46.24    68.42   42.67     14.18   -3.28
> > 80         46.37    63.13   41.62     7.43    -6.73
> > 96         46.40    63.31   42.20     9.36    -4.78
> > 128        50.43    62.79   42.16     13.11   -1.23
> > ________________________________________________________
> > BW: 37.2%,  CPU/RCPU: 66.3%,41.6%,  SD/RSD: 11.5%,-3.7%
> >
> > ______________ numtxqs=8, vhosts=5  ____________________
> > #sessions   BW%      CPU%     RCPU%     SD%      RSD%
> > ________________________________________________________
> > 1           -.76    -1.56     2.33      0        3.03
> > 2           17.41    11.11    11.41     0       -4.76
> > 4           42.12    55.11    30.20     19.51    .62
> > 8           54.69    80.00    39.22     24.39    -3.88
> > 16          54.77    81.62    40.89     20.34    -6.58
> > 24          54.66    79.68    41.57     15.49    -8.99
> > 32          54.92    76.82    41.79     17.59    -5.70
> > 40          51.79    68.56    40.53     15.31    -3.87
> > 48          51.72    66.40    40.84     9.72     -7.13
> > 64          51.11    63.94    41.10     5.93     -8.82
> > 80          46.51    59.50    39.80     9.33     -4.18
> > 96          47.72    57.75    39.84     4.20     -7.62
> > 128         54.35    58.95    40.66     3.24     -8.63
> > ________________________________________________________
> > BW: 38.9%,  CPU/RCPU: 63.0%,40.1%,  SD/RSD: 6.0%,-7.4%
> >
> > ______________ numtxqs=16, vhosts=5  ___________________
> > #sessions   BW%      CPU%     RCPU%     SD%      RSD%
> > ________________________________________________________
> > 1           -1.43    -3.52    1.55      0          3.03
> > 2           33.09     21.63   20.12    -10.00     -9.52
> > 4           67.17     94.60   44.28     19.51     -11.80
> > 8           75.72     108.14  49.15     25.00     -10.71
> > 16          80.34     101.77  52.94     25.93     -4.49
> > 24          70.84     93.12   43.62     27.63     -5.03
> > 32          69.01     94.16   47.33     29.68     -1.51
> > 40          58.56     63.47   25.91    -3.92      -25.85
> > 48          61.16     74.70   34.88     .89       -22.08
> > 64          54.37     69.09   26.80    -6.68      -30.04
> > 80          36.22     22.73   -2.97    -8.25      -27.23
> > 96          41.51     50.59   13.24     9.84      -16.77
> > 128         48.98     38.15   6.41     -.33       -22.80
> > ________________________________________________________
> > BW: 46.2%,  CPU/RCPU: 55.2%,18.8%,  SD/RSD: 1.2%,-22.0%
> >
> > ______________ numtxqs=32, vhosts=5  ___________________
> > #            BW%       CPU%    RCPU%    SD%     RSD%
> > ________________________________________________________
> > 1            7.62     -38.03   -26.26  -50.00   -33.33
> > 2            28.95     20.46    21.62   0       -7.14
> > 4            84.05     60.79    45.74  -2.43    -12.42
> > 8            86.43     79.57    50.32   15.85   -3.10
> > 16           88.63     99.48    58.17   9.47    -13.10
> > 24           74.65     80.87    41.99  -1.81    -22.89
> > 32           63.86     59.21    23.58  -18.13   -36.37
> > 40           64.79     60.53    22.23  -15.77   -35.84
> > 48           49.68     26.93    .51    -36.40   -49.61
> > 64           54.69     36.50    5.41   -26.59   -43.23
> > 80           45.06     12.72   -13.25  -37.79   -52.08
> > 96           40.21    -3.16    -24.53  -39.92   -52.97
> > 128          36.33    -33.19   -43.66  -5.68    -20.49
> > ________________________________________________________
> > BW: 49.3%,  CPU/RCPU: 15.5%,-8.2%,  SD/RSD: -22.2%,-37.0%
> >
> >
> > Signed-off-by: Krishna Kumar <[email-masked]>