On 01/31/2018 09:49 AM, J. Bruce Fields wrote:
On Tue, Jan 30, 2018 at 01:52:49PM -0600, Jeremy Linton wrote:
Have you tried this with a '-o nfsvers=3' during mount? Did that help?
I noticed a large decrease in my kernel build times across NFS/lan a while
back after a machine/kernel/10g upgrade. After playing with mount/export
options filesystem tuning/etc, I got to this point of timing a bunch of
these operations vs the older machine, at which point I discovered that
simply backing down to NFSv3 solved the problem.
AKA a nfsv3 server on a 10 year old 4 disk xfs RAID5 on 1Gb ethernet, was
slower than a modern machine with a 8 disk xfs RAID5 on 10Gb on nfsv4. The
effect was enough to change a kernel build from ~45 minutes down to less
than 5.
Did you mean "faster than"?
Yes, sorry about that.
Definitely worth trying, though I wouldn't expect it to make that big a
difference in the untarring-a-kernel-tree case--I think the only RPC
avoided in the v3 case would be the CLOSE, and it should be one of the
faster ones.
In the kernel compile case there's probably also a lot of re-opening and
re-reading files too? NFSv4 is chattier there too. Read delegations
should help compensate, but we need to improve the heuristics that
decide when they're given out.
The main kernel include files get repeatedly hammered, despite them in
theory being in cache, IIRC. So yes, if the concurrent (re)open path is
even slightly slower its going to hurt a lot.
All that aside I can't think what would explain that big a difference
(45 minutes vs. 5). It might be interesting to figure out what
happened.
I had already spent more than my time allotted looking in the wrong
direction at the filesystem/RAID (did turn off intellipark though) by
the time I discovered the nfsv3/v4 perf delta. Its been sitting way down
on the "things to look into" list for a long time now. I'm still using
it as a NFS server so at some point I can take another look if the
problem persists.
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