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SubjectRe: performance of filesystem xattrs with Samba4
From
Andrew,

> > Would anyone care to hazard a guess as to what aspect of -mm2 is
> > gaining us 10% in overall Samba4 performance?
>
> Is it reproducible with your tricked-up dbench?
>
> If so, please send me a machine description and the relevant command line
> and I'll do a bsearch.

Sorry for the delay in getting back to you on this. The full set of
runs for the data I posted last night took 12 hours to produce, so the
machine was a bit busy.

I've now confirmed that the new dbench does indeed show a significant
improvement in 2.6.10-rc2-mm2 as compared to
2.6.10-rc2. Interestingly, the improvement seems to be only in ext3,
which confused me for a while. The difference is also much more
dramatic (as a percentage) when xattrs are enabled in the test.

Here are the results for dbench3 runs with varying numbers of clients,
and with rc2 and rc2-mm2 for ext3. First the non-xattr results:

clients -rc2 rc2-mm2
-----------------------
10 362 376
20 328 357
30 249 270
40 169 199
50 128 155
60 107 143

now the xattr results (using the -x option to dbench)

clients -rc2 rc2-mm2
-----------------------
10 58 125
20 44 64
30 43 54
40 42 52
50 49 49
60 40 47

I don't know why there was no improvement at size 50.

for comparison, there is very little difference for xfs (or the other
filesystems I tested, which were jfs, reiser and ext2). Here are the
non-xattr xfs results:

clients -rc2 rc2-mm2
-----------------------
10 365 368
20 324 328
30 254 257
40 194 212
50 128 139
60 58 59

The script I used to run dbench is at
http://samba.org/~tridge/xattr_results/
the details on the machine config are there too.

For your bsearch, its probably best to choose one of the clearest
and least noisy results (like the xattr result for size 20) and just
run the search for that one. That will take a bit under 5 minutes per
test if you use the same runtime I did. You could do it quicker, but
you risk getting more noise in the results.

Cheers, Tridge
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