On Thu, Sep 4, 2014 at 3:39 PM, Chaitanya Huilgol
<[email protected]> wrote:
> Hi,
>
> In our benchmarking tests we observed that the ms_tcp_nodelay in ceph.conf
> option is not affecting the kernel rbd and as expected we see poor latency
> numbers for lower queue depths and 4K rand reads. There is significant
> increase in latency from qd=2 to 24 and starts tapering down for higher
> queue depths.
> We did not find relevant kernel_setsockopt with TCP_NODELAY in the kernel
> RBD/libceph (messenger.c) source. Unless we are missing something, looks like
> currently the kernel RBD is not setting this and this is affecting latency
> numbers are lower queue depths.
>
> I have tested with userspace fio(rbd engine) and rados bench and we see
> similar latency behavior when ms_tcp_nodelay is set to false. However setting
> this to true gives consistent low latency numbers for all queue depths
>
> Any ideas/thoughts on this?
>
> OS Ubuntu 14.04
> Kernel: 3.13.0-24-generic #46-Ubuntu SMP
> Ceph: Latest Master
No, we don't set TCP_NODELAY in the kernel client, but I think we can
add it as a rbd map/mount option. Sage?
Thanks,
Ilya
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