netdev - Re: [PATCH RFC v4 0/5] vhost: ring format independence

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Date:   Tue, 15 Oct 2019 10:58:13 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH RFC v4 0/5] vhost: ring format independence


On 2019/10/13 下午7:41, Michael S. Tsirkin wrote:
> This adds infrastructure required for supporting
> multiple ring formats.
>
> The idea is as follows: we convert descriptors to an
> independent format first, and process that converting to
> iov later.
>
> The point is that we have a tight loop that fetches
> descriptors, which is good for cache utilization.
> This will also allow all kind of batching tricks -
> e.g. it seems possible to keep SMAP disabled while
> we are fetching multiple descriptors.
>
> This seems to perform exactly the same as the original
> code already based on a microbenchmark.
> Lightly tested.
> More testing would be very much appreciated.
>
> To use new code:
> 	echo 1 > /sys/module/vhost_test/parameters/newcode
> or
> 	echo 1 > /sys/module/vhost_net/parameters/newcode
>
> changes from v3:
>          - fixed error handling in case of indirect descriptors
>          - add BUG_ON to detect buffer overflow in case of bugs
>                  in response to comment by Jason Wang
>          - minor code tweaks
>
> Changes from v2:
> 	- fixed indirect descriptor batching
>                  reported by Jason Wang
>
> Changes from v1:
> 	- typo fixes


I've just done some quick benchmark with testpmd + vhost_net txonly.

With 256 queue size, no difference but in 1024 queue size 1% regression 
of PPS were found.

Thanks


>
>
> Michael S. Tsirkin (5):
>    vhost: option to fetch descriptors through an independent struct
>    vhost/test: add an option to test new code
>    vhost: batching fetches
>    vhost/net: add an option to test new code
>    vhost: last descriptor must have NEXT clear
>
>   drivers/vhost/net.c   |  32 ++++-
>   drivers/vhost/test.c  |  19 ++-
>   drivers/vhost/vhost.c | 328 +++++++++++++++++++++++++++++++++++++++++-
>   drivers/vhost/vhost.h |  20 ++-
>   4 files changed, 385 insertions(+), 14 deletions(-)
>