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Date:   Mon, 20 Jul 2020 15:07:43 +0200
From:   Eugenio Perez Martin <eperezma@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        linux-kernel@...r.kernel.org, kvm list <kvm@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH RFC v8 02/11] vhost: use batched get_vq_desc version

On Mon, Jul 20, 2020 at 10:55 AM Jason Wang <jasowang@...hat.com> wrote:
>
>
> On 2020/7/17 上午1:16, Eugenio Perez Martin wrote:
> > On Fri, Jul 10, 2020 at 7:58 AM Michael S. Tsirkin <mst@...hat.com> wrote:
> >> On Fri, Jul 10, 2020 at 07:39:26AM +0200, Eugenio Perez Martin wrote:
> >>>>> How about playing with the batch size? Make it a mod parameter instead
> >>>>> of the hard coded 64, and measure for all values 1 to 64 ...
> >>>>
> >>>> Right, according to the test result, 64 seems to be too aggressive in
> >>>> the case of TX.
> >>>>
> >>> Got it, thanks both!
> >> In particular I wonder whether with batch size 1
> >> we get same performance as without batching
> >> (would indicate 64 is too aggressive)
> >> or not (would indicate one of the code changes
> >> affects performance in an unexpected way).
> >>
> >> --
> >> MST
> >>
> > Hi!
> >
> > Varying batch_size as drivers/vhost/net.c:VHOST_NET_BATCH,
>
>
> Did you mean varying the value of VHOST_NET_BATCH itself or the number
> of batched descriptors?
>
>
> > and testing
> > the pps as previous mail says. This means that we have either only
> > vhost_net batching (in base testing, like previously to apply this
> > patch) or both batching sizes the same.
> >
> > I've checked that vhost process (and pktgen) goes 100% cpu also.
> >
> > For tx: Batching decrements always the performance, in all cases. Not
> > sure why bufapi made things better the last time.
> >
> > Batching makes improvements until 64 bufs, I see increments of pps but like 1%.
> >
> > For rx: Batching always improves performance. It seems that if we
> > batch little, bufapi decreases performance, but beyond 64, bufapi is
> > much better. The bufapi version keeps improving until I set a batching
> > of 1024. So I guess it is super good to have a bunch of buffers to
> > receive.
> >
> > Since with this test I cannot disable event_idx or things like that,
> > what would be the next step for testing?
> >
> > Thanks!
> >
> > --
> > Results:
> > # Buf size: 1,16,32,64,128,256,512
> >
> > # Tx
> > # ===
> > # Base
> > 2293304.308,3396057.769,3540860.615,3636056.077,3332950.846,3694276.154,3689820
>
>
> What's the meaning of buf size in the context of "base"?
>

Hi Jason.

I think that all the previous questions have been answered in the
response to MST, please let me know if I missed something.

> And I wonder maybe perf diff can help.

Great, I will run it too.

Thanks!

>
> Thanks
>
>
> > # Batch
> > 2286723.857,3307191.643,3400346.571,3452527.786,3460766.857,3431042.5,3440722.286
> > # Batch + Bufapi
> > 2257970.769,3151268.385,3260150.538,3379383.846,3424028.846,3433384.308,3385635.231,3406554.538
> >
> > # Rx
> > # ==
> > # pktgen results (pps)
> > 1223275,1668868,1728794,1769261,1808574,1837252,1846436
> > 1456924,1797901,1831234,1868746,1877508,1931598,1936402
> > 1368923,1719716,1794373,1865170,1884803,1916021,1975160
> >
> > # Testpmd pps results
> > 1222698.143,1670604,1731040.6,1769218,1811206,1839308.75,1848478.75
> > 1450140.5,1799985.75,1834089.75,1871290,1880005.5,1934147.25,1939034
> > 1370621,1721858,1796287.75,1866618.5,1885466.5,1918670.75,1976173.5,1988760.75,1978316
> >
> > pktgen was run again for rx with 1024 and 2048 buf size, giving
> > 1988760.75 and 1978316 pps. Testpmd goes the same way.
> >
>

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