native libaio

[Volker Lendecke]

Hi!

In my wip branch on gitweb.samba.org 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 :-)

It's unlikely that we will be able to get the libaio
overhead down to zero, but those numbers might make it
possible to make aio the default.

Volker

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