linux-kernel - Re: [PATCH RFC 0/2] Packed ring for vhost

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Message-ID: <97e20ab7-a73c-e911-f5ae-38359f68d4f4@redhat.com>
Date:   Wed, 14 Feb 2018 11:48:08 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        wexu@...hat.com, jfreimann@...hat.com, tiwei.bie@...el.com
Subject: Re: [PATCH RFC 0/2] Packed ring for vhost



On 2018年02月14日 10:47, Michael S. Tsirkin wrote:
> On Wed, Feb 14, 2018 at 10:37:07AM +0800, Jason Wang wrote:
>> Hi all:
>>
>> This RFC implement a subset of packed ring which was described at
>> https://github.com/oasis-tcs/virtio-docs/blob/master/virtio-v1.1-packed-wd07.pdf
>> . The code were tested with pmd implement by Jens at
>> http://dpdk.org/ml/archives/dev/2018-January/089417.html. Minor
>> change was needed for pmd codes to kick virtqueue since it assumes a
>> busy polling backend.
>>
>> Test were done between localhost and guest. Testpmd (rxonly) in guest
>> reports 2.4Mpps. Testpmd (txonly) repots about 2.1Mpps.
> How does this compare with the split ring design?

No obvious difference (+-5%). I believe we reach the bottleneck of vhost.

>
>> It's not a complete implemention, here's what were missed:
>>
>> - Device Area
>> - Driver Area
>> - Descriptor indirection
>> - Zerocopy may not be functional
>> - Migration path is not tested
>> - Vhost devices except for net
>> - vIOMMU can not work (mainly because the metadata prefetch is not
>>    implemented).
>> - See FIXME/TODO in the codes for more details
>> - No batching or other optimizations were implemented
> ioeventfd for PIO/mmio/s390.
>

Probably, but this is not the stuffs of packed ring I think.

Thanks