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Subject: Re: [virtio-dev] Re: [virtio] [PATCH] ccw: split descriptor/available/used rings


"Michael S. Tsirkin" <mst@redhat.com> writes:
> On Tue, Oct 08, 2013 at 03:54:51PM +0200, Cornelia Huck wrote:
>> On Tue, 8 Oct 2013 15:39:25 +0200
>> Cornelia Huck <cornelia.huck@de.ibm.com> wrote:
>> 
>> > On Tue, 8 Oct 2013 16:07:18 +0300
>> > "Michael S. Tsirkin" <mst@redhat.com> wrote:
>> 
>> > > If we want drivers to do something we really must write it
>> > > explicitly.
>> > > 
>> > 
>> 
>> OK, here's what I've got:
>> 
>> commit 5a36ad2c5826ccf777d12b2183efc265c51015b0
>> Author: Cornelia Huck <cornelia.huck@de.ibm.com>
>> Date:   Tue Oct 8 15:49:36 2013 +0200
>> 
>>     virtio-ccw: clarify sense id operation
>>     
>>     Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
>
> Looks good to me.
> Only, please tweak subject next time you send a patch please :)
> It should look like this:

And feel free to commit this kind of clarification straight to the
repository.

Back to the actual subject of splitting the rings: we've already removed
the assumption that they will be contiguous from the core of the spec,
but that does not mean transports need to do the same.

The effect is to increase the ring size when large contiguous memory
ranges can't be obtained (eg. hotplug on long-running kernels).

(PAGESIZE=4096, ALIGN=4096)

Contiguous Pages        Max Qsz (unsplit)       Max Qsz (split)
1                       None                    256
2                       128                     512
3                       256                     512
4                       512                     1024
5                       512                     1024
6                       512                     1024
7                       1024                    1024
8                       1024                    2048

If this doesn't matter to you, it's almost certainly not worth the
hassle of changing.

Cheers,
Rusty.
PS.  I note that you expose KVM_VIRTIO_CCW_RING_ALIGN through uapi: that
seems unnecessary?



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