> As far as I can tell from the current test results,
> the writeback performance mostly stays on par with vanilla 3.1 kernel
> except for -14% regression on average for NFS, which can be cut down
> to -7% by limiting the commit size.
I find that the overall NFS throughput can be improved by 42% when
doing the NFS writeback wait queue and limiting the commit size.
3.1.0-rc8-ioless6+ 3.1.0-rc8-nfs-wq-smooth+
------------------------ ------------------------
22.43 +79.2% 40.20 NFS-thresh=100M/nfs-10dd-1M-32p-32768M-100M:10-X
28.21 +11.9% 31.58 NFS-thresh=100M/nfs-1dd-1M-32p-32768M-100M:10-X
29.21 +54.0% 44.98 NFS-thresh=100M/nfs-2dd-1M-32p-32768M-100M:10-X
14.12 +31.0% 18.50 NFS-thresh=10M/nfs-10dd-1M-32p-32768M-10M:10-X
29.44 +2.1% 30.06 NFS-thresh=10M/nfs-1dd-1M-32p-32768M-10M:10-X
9.09 +231.0% 30.07 NFS-thresh=10M/nfs-2dd-1M-32p-32768M-10M:10-X
25.68 +88.6% 48.43 NFS-thresh=1G/nfs-10dd-1M-32p-32768M-1024M:10-X
41.06 +14.9% 47.16 NFS-thresh=1G/nfs-1dd-1M-32p-32768M-1024M:10-X
39.13 +26.7% 49.56 NFS-thresh=1G/nfs-2dd-1M-32p-32768M-1024M:10-X
238.38 +42.9% 340.54 TOTAL
The theoretic explanation could be, one smooths out the NFS write
requests and the other smooths out the NFS commits, hence yielding
better utilized network/disk pipeline.
As a result, the -14% regression can be turned around into 23% speedup
comparing to vanilla kernel:
3.1.0-rc4-vanilla+ 3.1.0-rc8-nfs-wq-smooth+
------------------------ ------------------------
20.89 +92.5% 40.20 NFS-thresh=100M/nfs-10dd-1M-32p-32768M-100M:10-X
39.43 -19.9% 31.58 NFS-thresh=100M/nfs-1dd-1M-32p-32768M-100M:10-X
26.60 +69.1% 44.98 NFS-thresh=100M/nfs-2dd-1M-32p-32768M-100M:10-X
12.70 +45.7% 18.50 NFS-thresh=10M/nfs-10dd-1M-32p-32768M-10M:10-X
27.41 +9.7% 30.06 NFS-thresh=10M/nfs-1dd-1M-32p-32768M-10M:10-X
26.52 +13.4% 30.07 NFS-thresh=10M/nfs-2dd-1M-32p-32768M-10M:10-X
40.70 +19.0% 48.43 NFS-thresh=1G/nfs-10dd-1M-32p-32768M-1024M:10-X
45.28 +4.2% 47.16 NFS-thresh=1G/nfs-1dd-1M-32p-32768M-1024M:10-X
35.74 +38.7% 49.56 NFS-thresh=1G/nfs-2dd-1M-32p-32768M-1024M:10-X
275.28 +23.7% 340.54 TOTAL
The tests don't cover disk arrays on the server side, however it does
test various combinations of memory:bandwidth ratio.
Thanks,
Fengguang
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