Re: [PATCH net-next v4 0/4] vsock/virtio/vhost: MSG_ZEROCOPY preparations

[Arseniy Krasnov]

On 28.07.2023 08:45, Michael S. Tsirkin wrote:
> On Fri, Jul 28, 2023 at 01:26:23AM +0300, Arseniy Krasnov wrote:
>> Hello,
>>
>> this patchset is first of three parts of another big patchset for
>> MSG_ZEROCOPY flag support:
>> https://lore.kernel.org/netdev/20230701063947.3422088-1-AVKrasnov@xxxxxxxxxxxxxx/
> 
> overall looks good. Two points I'd like to see addressed:

Thanks!

> - what's the performance with all these changes - still same?

Yes, I perform quick tests and seems result are same. This is because last
implemented logic when I compare size of payload against 'num_max' is
for "emergency" case and not triggered in default environment. Anyway, I'll
perform retest at least in nested guest case.

> - most systems have a copybreak scheme where buffers
>   smaller than a given size are copied directly.
>   This will address regression you see with small buffers -
>   but need to find that value. we know it's between 4k and 32k :)

I see, You suggest to find this value and add this check for decision to
use zerocopy or copy ?

Thanks, Arseniy

> 
> 
>> During review of this series, Stefano Garzarella <sgarzare@xxxxxxxxxx>
>> suggested to split it for three parts to simplify review and merging:
>>
>> 1) virtio and vhost updates (for fragged skbs) <--- this patchset
>> 2) AF_VSOCK updates (allows to enable MSG_ZEROCOPY mode and read
>>    tx completions) and update for Documentation/.
>> 3) Updates for tests and utils.
>>
>> This series enables handling of fragged skbs in virtio and vhost parts.
>> Newly logic won't be triggered, because SO_ZEROCOPY options is still
>> impossible to enable at this moment (next bunch of patches from big
>> set above will enable it).
>>
>> I've included changelog to some patches anyway, because there were some
>> comments during review of last big patchset from the link above.
>>
>> Head for this patchset is 9d0cd5d25f7d45bce01bbb3193b54ac24b3a60f3
>>
>> Link to v1:
>> https://lore.kernel.org/netdev/20230717210051.856388-1-AVKrasnov@xxxxxxxxxxxxxx/
>> Link to v2:
>> https://lore.kernel.org/netdev/20230718180237.3248179-1-AVKrasnov@xxxxxxxxxxxxxx/
>> Link to v3:
>> https://lore.kernel.org/netdev/20230720214245.457298-1-AVKrasnov@xxxxxxxxxxxxxx/
>>
>> Changelog:
>>  * Patchset rebased and tested on new HEAD of net-next (see hash above).
>>  * See per-patch changelog after ---.
>>
>> Arseniy Krasnov (4):
>>   vsock/virtio/vhost: read data from non-linear skb
>>   vsock/virtio: support to send non-linear skb
>>   vsock/virtio: non-linear skb handling for tap
>>   vsock/virtio: MSG_ZEROCOPY flag support
>>
>>  drivers/vhost/vsock.c                   |  14 +-
>>  include/linux/virtio_vsock.h            |   6 +
>>  net/vmw_vsock/virtio_transport.c        |  79 +++++-
>>  net/vmw_vsock/virtio_transport_common.c | 312 ++++++++++++++++++------
>>  4 files changed, 330 insertions(+), 81 deletions(-)
>>
>> -- 
>> 2.25.1
>