Messages in this thread | | | From | Jeff Moyer <> | Subject | Re: [PATCH RESEND 5/5] vhost-blk: Add vhost-blk support | Date | Wed, 18 Jul 2012 10:31:28 -0400 |
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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.
Cheers, Jeff
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