[Samba] samba w/vfs notify_fam perf hit of 25% on writes noticed...?
samba at tlinx.org
Thu Feb 13 14:18:24 MST 2014
I was running some benchmarks and trying to tune speed between
a samba 3.6.22 server and win7.
My primary benchmark is using 'dd' on windows to read/write to
device files in my home directory to eliminate effects of disk latency.
So for reads, I transfer from h:/zero and for writes I write to h:/null.
Where h: is my unix home dir. (for the other end of the transfer,
I use /dev/null and /dev/zero, respectively, under cygwin).
I don't remember seeing this during previous benchmarks, which is
why I was more than a little curious.
When I'm doing the client write's
(writing 4G to the server, I used to see 98-99% cpu
usage from smbd that was servicing my session.
Now, I'm seeing about that amount from famd, and only in the upper
80%'s for smbd.
Transfer wise, I'm losing 25% on writes dropping them down to
around the same speed, or slightly less than 'reads' (writes
have normally been higher, cuz a writer with a large TCP
window can get ahead of where the reader is, but a reader
can never be ahead of what the writer has sent...).
So why is famd being peg'ed. My default write size is 8M,
count of 512. Even if samba called famd once/write, that'd
only be 512 times/second which should be negligible, but
it's acting more like it is getting called w/each packet?
Even that shouldn't be horrible, as I use a 9K packet size
to cut packet overhead by 5/6ths...
So wondering if anyone else has seen such or had experience
with famd -- especially in the most recent 3.6.22 series?
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