Emmanuel Florac wrote:
I noticed a long time ago that the thread information in
/proc/net/rpc/nfsd isn't updated anymore since somewhere between the
2.629 (information present) and 2.6.32 (information missing). It's
quite easy to check:
# grep th /proc/net/rpc/nfsd
th 8 0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
All values are perpetually at zero. Unsurprising, because the
update_thread_usage function in fs/nfsd/nfssvc.c isn't present anymore.
I can't find any information about why this information was dropped;
It's easy to find this information from the git log. It also shows up in the
top half dozen or so results of a Google search on the same term.
% git log --grep update_thread_usage
commit 8bbfa9f3889b643fc7de82c0c761ef17097f8faf
Author: Greg Banks <gnb@xxxxxxx>
Date: Tue Jan 13 21:26:34 2009 +1100
knfsd: remove the nfsd thread busy histogram
Stop gathering the data that feeds the 'th' line in /proc/net/rpc/nfsd
because the questionable data provided is not worth the scalability
impact of calculating it. Instead, always report zeroes. The current
approach suffers from three major issues:
1. update_thread_usage() increments buckets by call service
time or call arrival time...in jiffies. On lightly loaded
machines, call service times are usually < 1 jiffy; on
heavily loaded machines call arrival times will be << 1 jiffy.
So a large portion of the updates to the buckets are rounded
down to zero, and the histogram is undercounting.
2. As seen previously on the nfs mailing list, the format in which
the histogram is presented is cryptic, difficult to explain,
and difficult to use.
3. Updating the histogram requires taking a global spinlock and
dirtying the global variables nfsd_last_call, nfsd_busy, and
nfsdstats *twice* on every RPC call, which is a significant
scaling limitation.
Testing on a 4 CPU 4 NIC Altix using 4 IRIX clients each doing
1K streaming reads at full line rate, shows the stats update code
(inlined into nfsd()) takes about 1.7% of each CPU. This patch drops
the contribution from nfsd() into the profile noise.
This patch is a forward-ported version of knfsd-remove-nfsd-threadstats
which has been shipping in the SGI "Enhanced NFS" product since 2006.
In that time, exactly one customer has noticed that the threadstats
were missing. It has been previously posted:
http://article.gmane.org/gmane.linux.nfs/10376
and more recently requested to be posted again.
Signed-off-by: Greg Banks <gnb@xxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxxxxxx>
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