From: Paolo Bonzini <pbonzini@redhat.com>
To: Ming Lei <tom.leiming@gmail.com>, Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>,
"Michael S. Tsirkin" <mst@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux Virtualization <virtualization@lists.linux-foundation.org>
Subject: Re: [PATCH] virtio_blk: merge S/G list entries by default
Date: Wed, 10 Sep 2014 17:18:23 +0200 [thread overview]
Message-ID: <54106BBF.7010907@redhat.com> (raw)
In-Reply-To: <CACVXFVMRqgEh7EFQ0cDEatsqtxsgBrbSQNH9b6UZTsSD+=OWdA__14121.5735966854$1410309057$gmane$org@mail.gmail.com>
Il 07/09/2014 12:32, Ming Lei ha scritto:
> It is a good idea to disable SG merge for vq incapable of indirect because
> there are very limited direct descriptors.
I think you mean _enabling_ SG merge if indirect descriptors are not there.
> For vq capable of indirect, it should be better to not do SG merge at default
> because:
>
> - from hypervisor view, no matter how many segments one req has, all are
> submitted to host kernel by one syscall, such as readv/io_submit
>
> - host kernel still need to do the same merge again
Here we agree.
Paolo
> From my test(virtio-blk over null_blk), looks enabling SG merge may cause
> throughput a little drop(~3%).
next prev parent reply other threads:[~2014-09-10 15:18 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-06 23:09 [PATCH] virtio_blk: merge S/G list entries by default Christoph Hellwig
2014-09-07 10:18 ` Paolo Bonzini
2014-09-07 10:32 ` Ming Lei
2014-09-10 15:18 ` Paolo Bonzini [this message]
2014-09-10 15:21 ` Ming Lei
2014-09-07 11:41 ` Michael S. Tsirkin
2014-09-07 18:47 ` Christoph Hellwig
2014-09-08 8:18 ` Michael S. Tsirkin
2014-09-08 20:15 ` Christoph Hellwig
2014-09-10 16:43 ` Michael S. Tsirkin
2014-09-08 16:21 ` Paolo Bonzini
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