netdev - Re: [PATCH RFC v8 02/11] vhost: use batched get_vq

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Date:   Mon, 20 Jul 2020 16:55:20 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Eugenio Perez Martin <eperezma@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     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 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"?

And I wonder maybe perf diff can help.

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.
>