Messages in this thread | | | Date | Wed, 18 Jul 2012 22:45:58 +0800 | From | Asias He <> | Subject | Re: [PATCH RESEND 5/5] vhost-blk: Add vhost-blk support |
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On 07/18/2012 10:31 PM, Jeff Moyer wrote: > Asias He <asias@redhat.com> writes: > >> On 07/18/2012 03:10 AM, Jeff Moyer wrote: >>> Asias He <asias@redhat.com> writes: >>> >>>> vhost-blk is a in kernel virito-blk device accelerator. >>>> >>>> This patch is based on Liu Yuan's implementation with various >>>> improvements and bug fixes. Notably, this patch makes guest notify and >>>> host completion processing in parallel which gives about 60% performance >>>> improvement compared to Liu Yuan's implementation. >>> >>> So, first off, some basic questions. Is it correct to assume that you >>> tested this with buffered I/O (files opened *without* O_DIRECT)? >>> I'm pretty sure that if you used O_DIRECT, you'd run into problems (which >>> are solved by the patch set posted by Shaggy, based on Zach Brown's work >>> of many moons ago). Note that, with buffered I/O, the submission path >>> is NOT asynchronous. So, any speedups you've reported are extremely >>> suspect. ;-) >> >> I always used O_DIRECT to test this patchset. And I mostly used raw >> block device as guest image. Is this the reason why I did not hit the >> problem you mentioned. Btw, I do have run this patchset on image based >> file. I still do not see problems like IO hangs. > > Hmm, so do the iovec's passed in point to buffers in userspace? I > thought they were kernel buffers, which would have blown up in > get_user_pages_fast.
Yes. The iovec's passed in point to userspace buffers. ;-)
-- Asias
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