Limits on jumbo mbuf cluster allocation

[Andre Oppermann]

On 19.03.2013 05:29, Garrett Wollman wrote:
> <<On Tue, 12 Mar 2013 23:48:00 -0400 (EDT), Rick Macklem <rmacklem at uoguelph.ca> said:
>
>> I've attached a patch that has assorted changes.
>
> So I've done some preliminary testing on a slightly modified form of
> this patch, and it appears to have no major issues.  However, I'm
> still waiting for my user with 500 VMs to have enough free to be able
> to run some real stress tests for me.
>
> I was able to get about 2.5 Gbit/s throughput for a single streaming
> client over local 10G interfaces with jumbo frames (through a single
> switch and with LACP on both sides -- how well does lagg(4) interact
> with TSO and checksum offload?)  This is a little bit disappointing
> (considering that the filesystem can do 14 Gbit/s locally) but still
> pretty decent for one single-threaded client.  This obviously does not
> implicate the DRC changes at all, but does suggest that there is room
> for more performance improvement.  (In previous tests last year, I
> was able to get a sustained 8 Gbit/s when using multiple clients.)  I
> also found that one of our 10G switches is reordering TCP segments in
> a way that causes poor performance.

Of course testing a single vs. multiple clients has a different dynamic
on the control loop between TCP, RPC, NFS, VFS and disk.  The aggregate
multiple is likely to be much higher.  There may be optimization potential
in fine-tuning these control loops.

Also NFS (old and new) do not do direct dispatch of the VM pages as in
sendfile but copy the data into mbufs.  The performance improvement on
highly loaded systems may be non-trivial, however it is not so easy to
implement.

-- 
Andre

> I'll hopefully have some proper testing results later in the week.
>
> -GAWollman
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