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Subject: Re: [virtio-dev] Re: [virtio] [PATCH] ccw: split descriptor/available/used rings
On Tue, 15 Oct 2013 12:53:00 +1030 Rusty Russell <rusty@au1.ibm.com> wrote: > 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. Well, it sounds like a good thing to have, especially since we're likely to have both long running instances and a lot of hotplugging. I'd like to extend the communication structure though, like I did in my alternate proposal. I'll post a v2 without the special command reject handling. > > Cheers, > Rusty. > PS. I note that you expose KVM_VIRTIO_CCW_RING_ALIGN through uapi: that > seems unnecessary? virtio-pci exposes its alignment as well.
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