knfsd: remove the nfsd thread busy histogram (the 'th' line
in /proc/net/rc/nfsd) because the questionable data it provides
is not worth the scalability impact of calculating it. It
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 recently 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.
Signed-off-by: Greg Banks <[email protected]>
---
fs/nfsd/nfssvc.c | 32 --------------------------------
fs/nfsd/stats.c | 9 +--------
include/linux/nfsd/stats.h | 4 ----
3 files changed, 1 insertion(+), 44 deletions(-)
Index: linux-2.6.18-rc2/fs/nfsd/nfssvc.c
===================================================================
--- linux-2.6.18-rc2.orig/fs/nfsd/nfssvc.c 2006-08-04 16:09:30.526634953 +1000
+++ linux-2.6.18-rc2/fs/nfsd/nfssvc.c 2006-08-04 16:11:02.214864181 +1000
@@ -53,9 +53,6 @@ extern struct svc_program nfsd_program;
static void nfsd(struct svc_rqst *rqstp);
struct timeval nfssvc_boot;
struct svc_serv *nfsd_serv;
-static atomic_t nfsd_busy;
-static unsigned long nfsd_last_call;
-static DEFINE_SPINLOCK(nfsd_call_lock);
#if defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL)
static struct svc_stat nfsd_acl_svcstats;
@@ -199,7 +196,6 @@ int nfsd_create_serv(void)
return 0;
}
- atomic_set(&nfsd_busy, 0);
nfsd_serv = svc_create_pooled(&nfsd_program, NFSD_BUFSIZE,
nfsd_last_thread, nfsd,
SIG_NOCLEAN, THIS_MODULE);
@@ -347,26 +343,6 @@ nfsd_svc(unsigned short port, int nrserv
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
@@ -398,8 +374,6 @@ nfsd(struct svc_rqst *rqstp)
siginitsetinv(&shutdown_mask, SHUTDOWN_SIGS);
siginitsetinv(&allowed_mask, ALLOWED_SIGS);
- nfsdstats.th_cnt++;
-
rqstp->rq_task = current;
unlock_kernel();
@@ -427,8 +401,6 @@ nfsd(struct svc_rqst *rqstp)
;
if (err < 0)
break;
- update_thread_usage(atomic_read(&nfsd_busy));
- atomic_inc(&nfsd_busy);
/* Lock the export hash tables for reading. */
exp_readlock();
@@ -440,8 +412,6 @@ nfsd(struct svc_rqst *rqstp)
/* Unlock export hash tables */
exp_readunlock();
- update_thread_usage(atomic_read(&nfsd_busy));
- atomic_dec(&nfsd_busy);
}
if (err != -EINTR) {
@@ -460,8 +430,6 @@ nfsd(struct svc_rqst *rqstp)
lock_kernel();
- nfsdstats.th_cnt --;
-
out:
/* Release the thread */
svc_exit_thread(rqstp);
Index: linux-2.6.18-rc2/fs/nfsd/stats.c
===================================================================
--- linux-2.6.18-rc2.orig/fs/nfsd/stats.c 2006-07-16 07:53:08.000000000 +1000
+++ linux-2.6.18-rc2/fs/nfsd/stats.c 2006-08-04 16:11:02.218863668 +1000
@@ -55,16 +55,9 @@ static int nfsd_proc_show(struct seq_fil
nfsdstats.fh_nocache_nondir,
nfsdstats.io_read,
nfsdstats.io_write);
- /* thread usage: */
- seq_printf(seq, "th %u %u", nfsdstats.th_cnt, nfsdstats.th_fullcnt);
- for (i=0; i<10; i++) {
- unsigned int jifs = nfsdstats.th_usage[i];
- unsigned int sec = jifs / HZ, msec = (jifs % HZ)*1000/HZ;
- seq_printf(seq, " %u.%03u", sec, msec);
- }
/* newline and ra-cache */
- seq_printf(seq, "\nra %u", nfsdstats.ra_size);
+ seq_printf(seq, "ra %u", nfsdstats.ra_size);
for (i=0; i<11; i++)
seq_printf(seq, " %u", nfsdstats.ra_depth[i]);
seq_putc(seq, '\n');
Index: linux-2.6.18-rc2/include/linux/nfsd/stats.h
===================================================================
--- linux-2.6.18-rc2.orig/include/linux/nfsd/stats.h 2006-07-16 07:53:08.000000000 +1000
+++ linux-2.6.18-rc2/include/linux/nfsd/stats.h 2006-08-04 16:11:02.234861613 +1000
@@ -22,10 +22,6 @@ struct nfsd_stats {
unsigned int fh_nocache_nondir; /* filehandle not found in dcache */
unsigned int io_read; /* bytes returned to read requests */
unsigned int io_write; /* bytes passed in write requests */
- unsigned int th_cnt; /* number of available threads */
- unsigned int th_usage[10]; /* number of ticks during which n perdeciles
- * of available threads were in use */
- unsigned int th_fullcnt; /* number of times last free thread was used */
unsigned int ra_size; /* size of ra cache */
unsigned int ra_depth[11]; /* number of times ra entry was found that deep
* in the cache (10percentiles). [10] = not found */
Greg.
--
Greg Banks, R&D Software Engineer, SGI Australian Software Group.
I don't speak for SGI.
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