[Xen-devel] Odd blkdev throughput results

[Daniel Stodden <stodden@xxxxxxxxxx>]

Hi.

I've been running a couple of benchmarks on a Xen-3.0 installation
lately. Part of those compared SMP and CMP configurations on a 2x2 Intel
Woodcrest (i.e. two sockets). Tests were all performed between a UP dom0
(on core 0) and a UP domU and pinning the domU VCPU to core 1 (processor
0) or 3 (processor 1).

Switching from SMP to CMP, netperf -tTCP_TREAM gets me 1686.64 vs.
2673.20 Mbit/s. Lesser IPI latency, shared caches, all as one should
expect, I believe.

Now, trying that for block I/O may sound strange but can be done:
created a 3 GB ramdisk on dom0 and fed that to domU. peak with 'hdparm
-t' is at 759.37 MB/s on SMP.

The fun (for me, fun is probably a personal thing) part is that
throughput is higher than with TCP. May be due to the block layer being
much thinner than TCP/IP networking, or the fact that transfers utilize
the whole 4KB page size for sequential reads. Possibly some of both, I
didn't try.

This is not my question. What strikes me is that for the blkdev
interface, the CMP setup is 13% *slower* than SMP, at 661.99 MB/s.

Now, any ideas? I'm mildly familiar with both netback and blkback, and
I'd never expected something like that. Any hint appreciated.

Thanks,
Daniel

-- 
Daniel Stodden
LRR     -      Lehrstuhl für Rechnertechnik und Rechnerorganisation
Institut für Informatik der TU München             D-85748 Garching
http://www.lrr.in.tum.de/~stodden         mailto:stodden@xxxxxxxxxx
PGP Fingerprint: F5A4 1575 4C56 E26A 0B33  3D80 457E 82AE B0D8 735B



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