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xen-devel
Re: [Xen-devel] Re: userspace block backend / gntdev problems
Derek Murray <Derek.Murray@xxxxxxxxxxxx> writes:
> Hi Gerd,
>
> On 4 Jan 2008, at 13:48, Gerd Hoffmann wrote:
>> First problem is the fixed limit of 128 slots. The frontend
>> submits up
>> to 32 requests, with up to 11 grants each. With the shared ring this
>> sums up to 353 grants per block device. When is blkbackd running
>> in aio
>> mode, thus many requests are in flight at the same time and thus also
>> many grants mapped at the same time, the 128 limit is easily
>> reached. I
>> don't even need to stress the disk with bonnie or something, just
>> booting the virtual machine is enougth. Any chance replace the
>> fix-sized array with a list to remove that hard-coded limit? Or at
>> least raise the limit to -- say -- 1024 grants?
>
> The 128-grant limit is fairly arbitrary, and I wanted to see how
> people were using gntdev before changing this. The reason for using a
> fixed-size array is that it gives us O(1)-time mapping and unmapping
> of single grants, which I anticipated would be the most frequently-
> used case. I'll prepare a patch that enables the configuration of
> this limit when the device is opened.
Any news on this? I'd like to try converting the PV framebuffer to
use grants. I need to map ~2000-5000 pages, depending on the pvfb's
resolution.
[...]
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