Hi, Matt,
The point here is how to check donated frame done and where "free"
actually happens in domU. Currently Linux network driver utilizes zero-copy to
pass received packet up without any copy. In this case, the receive pages are
allocated from skbuff, which however is freed by upper layer instead of vnif
driver itself. To let dom0 know when the donated page is done, you may either:
- Copy content from donated page to local skbuff page, and then notify
dom0 immediately at the cost of performance
- Modify upper layer code to register "free" hook which notify dom0 if
done at the cost of more modification to common code and bias from x86.
Definitely there're other possibilities to make it "working" by this
approach and even more alternatives. However the point we really want to
emphasize here is that we can move towards x86 solution by adding PMT, with
best performance and less maintenance effort. That can actually minimize our
future re-base effort when para-drivers keep going. ;-)
Thanks,
Kevin
>-----Original Message-----
>From: Matt Chapman [mailto:matthewc@xxxxxxxxxxxxxxx]
>Sent: 2005年10月31日 13:09
>To: Tian, Kevin
>Cc: Dong, Eddie; xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
>Subject: Re: [Xen-ia64-devel] Re: PMT table for XEN/IA64 (was: RE:
>Transparentparavirtualization vs. xen paravirtualization)
>
>Yes, I think I understand the problem now.
>
>The way I imagine this could work is that Dom0 would know about all
>of the memory in the machine (i.e. it would be passed the original
>EFI memmap, minus memory used by Xen).
>
>Then Dom0 would donate memory for other domains (=ballooning).
>Dom0 can donate data frames to DomU in the same way - by granting
>the frame and not freeing it. When DomU donates a data frame to
>Dom0, Dom0 frees it when it is done, and now the kernel can use it.
>
>What do you think of this approach?
>
>Matt
>
>
>On Mon, Oct 31, 2005 at 11:09:04AM +0800, Tian, Kevin wrote:
>> Hi, Matt,
>> It's not related to mapped virtual address, but only for
>> physical/machine pfn.
>Current vnif backend (on x86) works as:
>>
>> 1. Allocate a set of physical pfns from kernel
>> 2. chop up the mapping between physical pfn and old machine pfn
>> 3. Transfer ownership of old machine pfn to frontend
>> 4. Allocate new machine pfn and bound to that physical pfn
>> (In this case, there's no ownership return from frontend for performance
>> reason)
>>
>> If without PMT table (Assuming guest==machine for dom0), that means you
>have to hotplug physical pfns from guest (based on page granularity) based on
>current vnif model. Or maybe you have better alternative without PMT, and
>without
>big change to existing vnif driver simultaneously?
>>
>> Thanks,
>> Kevin
>>
>> >-----Original Message-----
>> >From: xen-ia64-devel-bounces@xxxxxxxxxxxxxxxxxxx
>> >[mailto:xen-ia64-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Matt
>Chapman
>> >Sent: 2005年10月31日 10:59
>> >To: Dong, Eddie
>> >Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
>> >Subject: [Xen-ia64-devel] Re: PMT table for XEN/IA64 (was: RE:
>> >Transparentparavirtualization vs. xen paravirtualization)
>> >
>> >Hi Eddie,
>> >
>> >The way I did it was to make the address argument to grant
>> >hypercalls in/out; that is, the hypervisor might possibly return
>> >a different address than the one requested, like mmap on UNIX.
>> >
>> >For DomU, the hypervisor would map the page at the requested
>> >address. For Dom0, the hypervisor would instead return the
>> >existing address of that page, since Dom0 already has access
>> >to the whole address space.
>> >
>> >(N.B. I'm referring to physical/machine mappings here; unlike
>> >the x86 implementation where the grant table ops map pages
>> >directly into virtual address space).
>> >
>> >Matt
>> >
>> >
>> >On Fri, Oct 28, 2005 at 10:28:08PM +0800, Dong, Eddie wrote:
>> >> > Page flipping should work just fine
>> >> > in the current design; Matt had it almost working (out of tree)
>> >> > before he went back to school.
>> >> >
>> >> Matt:
>> >> Dan mentioned that you had VNIF work almost done without PMT
>> >> table support for dom0, Can you share the idea with us?
>> >> Usually VNIF swap page between dom0 and domU so that network
>> >> package copy (between dom0 native driver and domU frontend driver) can
>> >> be avoided and thus achieve high performance. With this swap, we can no
>> >> longer assume dom0 gpn=mfn. So what did you ever propose to port VNIF
>> >> without PMT table?
>> >> Thanks a lot, eddie
>> >
>> >_______________________________________________
>> >Xen-ia64-devel mailing list
>> >Xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
>> >http://lists.xensource.com/xen-ia64-devel
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