From 8bbfa9f3889b643fc7de82c0c761ef17097f8faf Mon Sep 17 00:00:00 2001 From: Greg Banks Date: Tue, 13 Jan 2009 21:26:34 +1100 Subject: [PATCH] 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 Signed-off-by: J. Bruce Fields --- fs/nfsd/nfssvc.c | 28 ---------------------------- 1 file changed, 28 deletions(-) diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c index 07e4f5d7baa..c3eb0759fd5 100644 --- a/fs/nfsd/nfssvc.c +++ b/fs/nfsd/nfssvc.c @@ -40,9 +40,6 @@ extern struct svc_program nfsd_program; static int nfsd(void *vrqstp); struct timeval nfssvc_boot; -static atomic_t nfsd_busy; -static unsigned long nfsd_last_call; -static DEFINE_SPINLOCK(nfsd_call_lock); /* * nfsd_mutex protects nfsd_serv -- both the pointer itself and the members @@ -227,7 +224,6 @@ int nfsd_create_serv(void) nfsd_max_blksize /= 2; } - atomic_set(&nfsd_busy, 0); nfsd_serv = svc_create_pooled(&nfsd_program, nfsd_max_blksize, AF_INET, nfsd_last_thread, nfsd, THIS_MODULE); @@ -376,26 +372,6 @@ nfsd_svc(unsigned short port, int nrservs) return error; } -static inline void -update_thread_usage(int busy_threads) -{ - unsigned long prev_call; - unsigned long diff; - int decile; - - spin_lock(&nfsd_call_lock); - prev_call = nfsd_last_call; - nfsd_last_call = jiffies; - decile = busy_threads*10/nfsdstats.th_cnt; - if (decile>0 && decile <= 10) { - diff = nfsd_last_call - prev_call; - if ( (nfsdstats.th_usage[decile-1] += diff) >= NFSD_USAGE_WRAP) - nfsdstats.th_usage[decile-1] -= NFSD_USAGE_WRAP; - if (decile == 10) - nfsdstats.th_fullcnt++; - } - spin_unlock(&nfsd_call_lock); -} /* * This is the NFS server kernel thread @@ -464,8 +440,6 @@ nfsd(void *vrqstp) continue; } - update_thread_usage(atomic_read(&nfsd_busy)); - atomic_inc(&nfsd_busy); /* Lock the export hash tables for reading. */ exp_readlock(); @@ -474,8 +448,6 @@ nfsd(void *vrqstp) /* Unlock export hash tables */ exp_readunlock(); - update_thread_usage(atomic_read(&nfsd_busy)); - atomic_dec(&nfsd_busy); } /* Clear signals before calling svc_exit_thread() */ -- 2.41.1