native libaio

Volker Lendecke Volker.Lendecke at SerNet.DE
Sun Jun 13 15:41:49 MDT 2010

On Sun, Jun 13, 2010 at 05:37:24PM +0200, Volker Lendecke wrote:
> In my wip branch on I've got code to call
> libaio (using native linux aio) for read&x. I've got some
> numbers for reading 1GB (out of cache) with smbclient on TCP
> loopback on a 4-core system. User/sys times are smbd -d 0 -i
> times.
> sync I/O:
> user    0m0.072s
> sys     0m0.716s
> 817284,4 MByte/s
> libaio async I/O:
> user    0m0.124s
> sys     0m0.796s
> 742617,5 MByte/s
> posix AIO:
> user    0m0.300s
> sys     0m1.600s
> 461724,3 MByte/s
> This means the native linux aio is in fact a hell lot faster
> than the glibc implementation :-)

Crap. Bjoern just pointed out that all this might be a pure
fallacy. In you can
read that libaio is only asynch if we use DIRECTIO. That
sucks. Severely. I've done some benchmarking with the pure
clone-based implementation in libaio, and to me it seems
that the context switches between the main and the worker
threads really kill the performance. Well, what can you do.


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