Messages in this thread | | | Date | Mon, 01 Aug 2011 17:18:02 +0800 | From | Liu Yuan <> | Subject | Re: [RFC PATCH]vhost-blk: In-kernel accelerator for virtio block device |
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On 08/01/2011 04:17 PM, Avi Kivity wrote: > On 07/29/2011 06:25 PM, Sasha Levin wrote: >> On Fri, 2011-07-29 at 20:01 +0800, Liu Yuan wrote: >> > Looking at this long list,most are function pointers that can not be >> > inlined, and the internal data structures used by these functions are >> > dozons. Leave aside code complexity, this long code path would really >> > need retrofit. As Christoph simply put, this kind of mess is inherent >> > all over the qemu code. So I am afraid, the 'retrofit' would end >> up to >> > be a re-write the entire (sub)system. I have to admit that, I am >> > inclined to the MST's vhost approach, that write a new subsystem >> other >> > than tedious profiling and fixing, that would possibly goes as far as >> > actually re-writing it. >> >> I don't think the fix for problematic userspace is to write more kernel >> code. >> >> vhost-net improved throughput and latency by several factors, allowing >> to achieve much more than was possible at userspace alone. >> >> With vhost-blk we see an improvement of ~15% - which I assume by your >> and Christoph's comments can be mostly attributed to QEMU. Merging a >> module which won't improve performance dramatically compared to what is >> possible to achieve in userspace (even if it would require a code >> rewrite) sounds a bit wrong to me > > Agree. vhost-net works around the lack of async zero copy networking > interface. Block I/O on the other hand does have such an interface, > and in addition transaction rates are usually lower. All we're saving > is the syscall overhead. > Personally I too agree with Sasha Levin. But vhost-blk is the first fast prototype that is supposed to act as a code base to do further optimisation, which I plan to utilize kernel's internal stuff like BIO layer, that can not be accessed from user space, to maximize the performance for raw disk based block IO.
Yuan
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