netdev - Re: [PATCH 2/3] virtio: indirect ring entries (VIRTIO_RING_F_INDIRECT

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 21 Apr 2009 13:59:05 +0100
From:	Mark McLoughlin <markmc@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	Avi Kivity <avi@...hat.com>, Dor Laor <dor@...hat.com>
Subject: Re: [PATCH 2/3] virtio: indirect ring entries
 (VIRTIO_RING_F_INDIRECT_DESC)

Hi Rusty,

On Thu, 2008-12-18 at 17:10 +0000, Mark McLoughlin wrote:
> Add a new feature flag for indirect ring entries. These are ring
> entries which point to a table of buffer descriptors.
> 
> The idea here is to increase the ring capacity by allowing a larger
> effective ring size whereby the ring size dictates the number of
> requests that may be outstanding, rather than the size of those
> requests.
> 
> This should be most effective in the case of block I/O where we can
> potentially benefit by concurrently dispatching a large number of
> large requests. Even in the simple case of single segment block
> requests, this results in a threefold increase in ring capacity.

Apparently, this would also be useful for the windows virtio-net
drivers.

Dor can explain further, but apparently Windows has been observed
passing the driver a packet with >256 fragments when using TSO.

With a ring size of 256, the guest can either drop the packet or copy it
into a single buffer. We'd much rather if we could use an indirect ring
entry to pass this number of fragments without copying.

For reference the original patch was here:

  http://lkml.org/lkml/2008/12/18/212

Cheers,
Mark.

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html