Messages in this thread | | | Date | Mon, 01 Aug 2011 11:17:51 +0300 | From | Avi Kivity <> | Subject | Re: [RFC PATCH]vhost-blk: In-kernel accelerator for virtio block device |
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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.
-- error compiling committee.c: too many arguments to function
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