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From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org
Subject: Re: [PATCH RFC v1 0/2] vhost: ring format independence
Date: Sat, 12 Oct 2019 16:15:42 +0800
Message-ID: <f650ac1a-6e2a-9215-6e4f-a1095f4a89cd@redhat.com> (raw)
In-Reply-To: <20191011134358.16912-1-mst@redhat.com>


On 2019/10/11 下午9:45, Michael S. Tsirkin wrote:
> So 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.


I wonder this may help for performance:

- another indirection layer, increased footprint

- won't help or even degrade when there's no batch

- an extra overhead in the case of in order where we should already had 
tight loop

- need carefully deal with indirect and chain or make it only work for 
packet sit just in a single descriptor

Thanks


>
> And perhaps more importantly, this is a very good fit for the packed
> ring layout, where we get and put descriptors in order.
>
> This patchset seems to already perform exactly the same as the original
> code already based on a microbenchmark.  More testing would be very much
> appreciated.
>
> Biggest TODO before this first step is ready to go in is to
> batch indirect descriptors as well.
>
> Integrating into vhost-net is basically
> s/vhost_get_vq_desc/vhost_get_vq_desc_batch/ -
> or add a module parameter like I did in the test module.
>
>
>
> Michael S. Tsirkin (2):
>    vhost: option to fetch descriptors through an independent struct
>    vhost: batching fetches
>
>   drivers/vhost/test.c  |  19 ++-
>   drivers/vhost/vhost.c | 333 +++++++++++++++++++++++++++++++++++++++++-
>   drivers/vhost/vhost.h |  20 ++-
>   3 files changed, 365 insertions(+), 7 deletions(-)
>

  parent reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-11 13:45 Michael S. Tsirkin
2019-10-11 13:45 ` [PATCH RFC v1 1/2] vhost: option to fetch descriptors through an independent struct Michael S. Tsirkin
2019-10-12  7:28   ` Jason Wang
2019-10-12 20:27     ` Michael S. Tsirkin
2019-10-14  1:43       ` Jason Wang
2019-10-15 20:20         ` Michael S. Tsirkin
2019-10-16  4:38           ` Jason Wang
2019-10-11 13:46 ` [PATCH RFC v1 2/2] vhost: batching fetches Michael S. Tsirkin
2019-10-12  7:30   ` Jason Wang
2019-10-12 20:36     ` Michael S. Tsirkin
2019-10-14  1:47       ` Jason Wang
2019-10-12  7:31 ` [PATCH RFC v1 0/2] vhost: ring format independence Jason Wang
2019-10-12 20:36   ` Michael S. Tsirkin
2019-10-12  8:15 ` Jason Wang [this message]
2019-10-12 19:26   ` Michael S. Tsirkin

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