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Subject[patch] nfsd optimizations for test10 (yet another try)
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Neil,

Here is a set of fixes and answers to you questions/points. The new patch
was tested in my own environment again and worked fine.


1/ Why did you change nfsd_busy into an atomic_t? It is only ever
used or updated inside the Big-Kernel-Lock, so it doesn't need
to be atomic.

I think I described why this was there in the previous email.

2/ Your new nfsd_racache_init always allocates a new cache, were as
the current one checks first to see if it has already been
allocated.
This is important because it is quite legal to run "rpc.nfsd"
multiple times. Subsequent invocations serve to change the number
of nfsd threads running.

Fixed.


3/ You currently allocate a single slab of memory for all of the
"struct raparms". Admittedly this is what the old code did, but I
don't think that it is really necessary, and calling kmalloc
multiple times would work just a well and would (arguably) be
clearer.

Changed to use kmalloc.


4/ small point: you added a hash table as the comment suggests might
be needed, but you didn't change the comment accordingly:-)

Fixed (but didn't add much comment since it seems to be so
straight-forward).

5/ the calls to spin_lock/spin_unlock in nfsd_racache_init seem
pointless. At this point, nothing else could possibly be accessing
the racache, and if it was you would have even bigger problems.
ditto for nfsd_racache_shutdown

Fixed.

6/ The lru list is now a list.h list, but the hash lists aren't. Why
is that?

Fixed.

7/ The old code kept a 'use' count for each cache entry to make sure
that an entry was not reused while it was in use. You have dropped
this. Now because of the lru ordering, and because each thread can
use at most one entry, you wont have a problem if there are more
cache entries than threads, and you currently have 2048 entries
configured which is greater than NFSD_MAXSERVS. However I think it
would be best if this dependancy were made explicit.
Maybe the call to nfsd_racache_init should tell the racache how
many threads are being started, and nfsd_racache_init should record
how many cache entries have been alloced, and it could alloc some
more if needed.

I'd disagree on creating dependancy between # of NFSD threads and cache
entries.
The # of cache entries is more a function of open/read files than anything
else.
Of course, you can argue that more NFSD threads could mean a larger # of
files, but
using a sensible number (like 2048) would suffice for a huge number of NFSD
threads.
In practice, more than several hundreds of NFSD threads will probably never
happen, even on
large SMPs. Also, since 2048 entries really do not take much memory (couple
of hundred KBs),
it seems to be ok to simply go with it.

8/ I would like the stats collected to tell me a bit more about what
was going on. If find simple hit/miss numbers nearly useless, as
you expect many lookups to be misses anyway (first time a file is
accessed) but you don't know what percentage.
As a first approximation, I would like to only count a miss if the
seek address was > 0.
What would be really nice would be to get stats on how long entries
stayed in the cache between last use and re-use. If we stored a
'last-use' time in each entry, and on reuse, kept count of which
range the age was is:

0-62 msec
63-125 msec
125-250 msec
250-500 msec
500-1000 msec
1-2 sec
2-4 sec
4-8 sec
8-16 sec
16-32 sec

This obviously isn't critical, but it would be nice to be able
to see how the cache was working.

Sure. I haven't put in such things in this patch. I'd be happy to roll such
things in later on, since it's non-critical
at the moment.

9/ Actually, you don't need the spinlock at all, and nfsd is currently
all under the BigKernelLock, but it doesn't hurt to have it around
the nfsd_get_raparms function because we hopefully will get rid of
the BKL one day.

Again, I explained why I had it in the previous email.

Regards,

Ying

Here is the patch. The only files changed since the last patch were
racache.h and nfsracache.c.
========================================================
diff -ruN nfsd.orig/nfsd.h nfsd.opt/nfsd.h
--- nfsd.orig/nfsd.h Fri Nov 10 15:27:37 2000
+++ nfsd.opt/nfsd.h Fri Nov 10 16:03:43 2000
@@ -76,7 +76,7 @@

/* nfsd/vfs.c */
int fh_lock_parent(struct svc_fh *, struct dentry *);
-int nfsd_racache_init(int);
+int nfsd_racache_init(void);
void nfsd_racache_shutdown(void);
int nfsd_lookup(struct svc_rqst *, struct svc_fh *,
const char *, int, struct svc_fh *);
diff -ruN nfsd.orig/racache.h nfsd.opt/racache.h
--- nfsd.orig/racache.h Fri Nov 10 16:10:23 2000
+++ nfsd.opt/racache.h Fri Nov 10 15:50:49 2000
@@ -0,0 +1,41 @@
+/*
+ * include/linux/nfsd/racache.h
+ *
+ * Read ahead racache.
+ */
+
+#ifndef NFSRACACHE_H
+#define NFSRACACHE_H
+
+#ifdef __KERNEL__
+#include <linux/sched.h>
+
+/*
+ * This is a cache of readahead params that help us choose the proper
+ * readahead strategy. Initially, we set all readahead parameters to 0
+ * and let the VFS handle things.
+ * If you increase the number of cached files very much, you'll need to
+ * add a hash table here.
+ */
+/*
+ * Representation of an racache entry. The first two members *must*
+ * be hash_next and hash_prev.
+ */
+struct raparms {
+ struct list_head p_hash;
+ struct list_head p_lru;
+ ino_t p_ino;
+ dev_t p_dev;
+ unsigned long p_reada,
+ p_ramax,
+ p_raend,
+ p_ralen,
+ p_rawin;
+};
+
+int nfsd_racache_init(void);
+void nfsd_racache_shutdown(void);
+struct raparms *nfsd_get_raparms(dev_t , ino_t );
+
+#endif /* __KERNEL__ */
+#endif /* NFSRACACHE_H */
diff -ruN nfsd.orig/stats.h nfsd.opt/stats.h
--- nfsd.orig/stats.h Tue Jul 18 23:04:06 2000
+++ nfsd.opt/stats.h Fri Nov 10 15:51:52 2000
@@ -25,8 +25,8 @@
* 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 */
+ unsigned int ra_hits; /* ra cache hits */
+ unsigned int ra_misses; /* ra cache misses */
};

/* thread usage wraps very million seconds (approx one fortnight) */
diff -ruN nfsd.orig/Makefile nfsd.opt/Makefile
--- nfsd.orig/Makefile Wed Dec 8 15:17:55 1999
+++ nfsd.opt/Makefile Fri Nov 10 17:10:56 2000
@@ -9,7 +9,7 @@

O_TARGET := nfsd.o
O_OBJS := nfssvc.o nfsctl.o nfsproc.o nfsfh.o vfs.o \
- export.o auth.o lockd.o nfscache.o nfsxdr.o \
+ export.o auth.o lockd.o nfscache.o nfsracache.o nfsxdr.o \
stats.o
ifdef CONFIG_NFSD_V3
O_OBJS += nfs3proc.o nfs3xdr.o
diff -ruN nfsd.orig/nfssvc.c nfsd.opt/nfssvc.c
--- nfsd.orig/nfssvc.c Sun Oct 1 20:35:16 2000
+++ nfsd.opt/nfssvc.c Fri Nov 10 17:03:09 2000
@@ -43,7 +43,7 @@
static void nfsd(struct svc_rqst *rqstp);
struct timeval nfssvc_boot;
static struct svc_serv *nfsd_serv;
-static int nfsd_busy;
+static atomic_t nfsd_busy;
static unsigned long nfsd_last_call;

struct nfsd_list {
@@ -72,7 +72,7 @@
nrservs = NFSD_MAXSERVS;

/* Readahead param cache - will no-op if it already exists */
- error = nfsd_racache_init(2*nrservs);
+ error = nfsd_racache_init();
if (error<0)
goto out;
if (!nfsd_serv) {
@@ -185,8 +185,8 @@
;
if (err < 0)
break;
- update_thread_usage(nfsd_busy);
- nfsd_busy++;
+ update_thread_usage(atomic_read(&nfsd_busy));
+ atomic_inc(&nfsd_busy);

/* Lock the export hash tables for reading. */
exp_readlock();
@@ -205,8 +205,8 @@

/* Unlock export hash tables */
exp_unlock();
- update_thread_usage(nfsd_busy);
- nfsd_busy--;
+ update_thread_usage(atomic_read(&nfsd_busy));
+ atomic_dec(&nfsd_busy);
}

if (err != -EINTR) {
diff -ruN nfsd.orig/stats.c nfsd.opt/stats.c
--- nfsd.orig/stats.c Tue Jul 18 23:04:06 2000
+++ nfsd.opt/stats.c Fri Nov 10 17:04:52 2000
@@ -15,9 +15,8 @@
* th <threads> <fullcnt> <10%-20%> <20%-30%> ... <90%-100%> <100%>
* time (seconds) when nfsd thread usage above thresholds
* and number of times that all threads were in use
- * ra cache-size <10% <20% <30% ... <100% not-found
- * number of times that read-ahead entry was found that deep in
- * the cache.
+ * ra cache-size <racache-size> <hits> <misses>
+ racache size, hits, and misses
* plus generic RPC stats (see net/sunrpc/stats.c)
*
* Copyright (C) 1995, 1996, 1997 Olaf Kirch <okir@monad.swb.de>
@@ -65,11 +64,8 @@
}

/* newline and ra-cache */
- len += sprintf(buffer+len, "\nra %u", nfsdstats.ra_size);
- for (i=0; i<11; i++)
- len += sprintf(buffer+len, " %u", nfsdstats.ra_depth[i]);
- len += sprintf(buffer+len, "\n");
-
+ len += sprintf(buffer+len, "\nra %u %u %u\n", nfsdstats.ra_size,
+ nfsdstats.ra_hits, nfsdstats.ra_misses);

/* Assume we haven't hit EOF yet. Will be set by svc_proc_read. */
*eof = 0;
diff -ruN nfsd.orig/vfs.c nfsd.opt/vfs.c
--- nfsd.orig/vfs.c Mon Oct 16 12:58:51 2000
+++ nfsd.opt/vfs.c Fri Nov 10 17:09:23 2000
@@ -36,6 +36,7 @@

#include <linux/sunrpc/svc.h>
#include <linux/nfsd/nfsd.h>
+#include <linux/nfsd/racache.h>
#ifdef CONFIG_NFSD_V3
#include <linux/nfs3.h>
#include <linux/nfsd/xdr3.h>
@@ -56,28 +57,6 @@
#define IS_ISMNDLK(i) (S_ISREG((i)->i_mode) && MANDATORY_LOCK(i))

/*
- * This is a cache of readahead params that help us choose the proper
- * readahead strategy. Initially, we set all readahead parameters to 0
- * and let the VFS handle things.
- * If you increase the number of cached files very much, you'll need to
- * add a hash table here.
- */
-struct raparms {
- struct raparms *p_next;
- unsigned int p_count;
- ino_t p_ino;
- dev_t p_dev;
- unsigned long p_reada,
- p_ramax,
- p_raend,
- p_ralen,
- p_rawin;
-};
-
-static struct raparms * raparml;
-static struct raparms * raparm_cache;
-
-/*
* Look up one component of a pathname.
* N.B. After this call _both_ fhp and resfh need an fh_put
*
@@ -540,42 +519,6 @@
}

/*
- * Obtain the readahead parameters for the file
- * specified by (dev, ino).
- */
-static inline struct raparms *
-nfsd_get_raparms(dev_t dev, ino_t ino)
-{
- struct raparms *ra, **rap, **frap = NULL;
- int depth = 0;
-
- for (rap = &raparm_cache; (ra = *rap); rap = &ra->p_next) {
- if (ra->p_ino == ino && ra->p_dev == dev)
- goto found;
- depth++;
- if (ra->p_count == 0)
- frap = rap;
- }
- depth = nfsdstats.ra_size*11/10;
- if (!frap)
- return NULL;
- rap = frap;
- ra = *frap;
- memset(ra, 0, sizeof(*ra));
- ra->p_dev = dev;
- ra->p_ino = ino;
-found:
- if (rap != &raparm_cache) {
- *rap = ra->p_next;
- ra->p_next = raparm_cache;
- raparm_cache = ra;
- }
- ra->p_count++;
- nfsdstats.ra_depth[depth*10/nfsdstats.ra_size]++;
- return ra;
-}
-
-/*
* Read data from a file. count must contain the requested read count
* on entry. On return, *count contains the number of bytes actually read.
* N.B. After this call fhp needs an fh_put
@@ -626,7 +569,6 @@
ra->p_raend = file.f_raend;
ra->p_ralen = file.f_ralen;
ra->p_rawin = file.f_rawin;
- ra->p_count -= 1;
}

if (err >= 0) {
@@ -1546,42 +1488,4 @@
err = permission(inode, MAY_EXEC);

return err? nfserrno(err) : 0;
-}
-
-void
-nfsd_racache_shutdown(void)
-{
- if (!raparm_cache)
- return;
- dprintk("nfsd: freeing readahead buffers.\n");
- kfree(raparml);
- raparm_cache = raparml = NULL;
-}
-/*
- * Initialize readahead param cache
- */
-int
-nfsd_racache_init(int cache_size)
-{
- int i;
-
- if (raparm_cache)
- return 0;
- raparml = kmalloc(sizeof(struct raparms) * cache_size, GFP_KERNEL);
-
- if (raparml != NULL) {
- dprintk("nfsd: allocating %d readahead buffers.\n",
- cache_size);
- memset(raparml, 0, sizeof(struct raparms) * cache_size);
- for (i = 0; i < cache_size - 1; i++) {
- raparml[i].p_next = raparml + i + 1;
- }
- raparm_cache = raparml;
- } else {
- printk(KERN_WARNING
- "nfsd: Could not allocate memory read-ahead cache.\n");
- return -ENOMEM;
- }
- nfsdstats.ra_size = cache_size;
- return 0;
}
diff -ruN nfsd.orig/nfsracache.c nfsd.opt/nfsracache.c
--- nfsd.orig/nfsracache.c Fri Nov 10 16:10:23 2000
+++ nfsd.opt/nfsracache.c Fri Nov 10 15:50:49 2000
@@ -0,0 +1,150 @@
+/*
+ * linux/fs/nfsd/nfsracache.c
+ *
+ * NFSD racache.
+ */
+
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/malloc.h>
+#include <linux/string.h>
+
+#include <linux/sunrpc/svc.h>
+#include <linux/nfsd/nfsd.h>
+#include <linux/nfsd/racache.h>
+
+#define CACHESIZE 2048
+#define HASHSIZE 512
+#define REQHASH(ino, dev) ((((ino) >> 24) ^ (ino) ^ (dev)) & (HASHSIZE-1))
+
+spinlock_t racache_lock = SPIN_LOCK_UNLOCKED;
+static struct raparms * raparm_cache = NULL;
+static struct list_head * hash_list;
+static struct list_head lru_head;
+static struct list_head free_head;
+static unsigned long racache_init = 0;
+
+int
+nfsd_racache_init(void)
+{
+ struct raparms *rp;
+ struct list_head *rahead;
+ size_t i;
+
+ if (racache_init)
+ return;
+ i = CACHESIZE * sizeof (struct raparms);
+ while (1) {
+ raparm_cache = (struct raparms *)kmalloc(i, GFP_KERNEL);
+ if (!raparm_cache)
+ i /= 2;
+ else
+ break;
+ if (i == 0) {
+ printk (KERN_ERR "nfsd: cannot allocate space for racache\n");
+ return -1;
+ }
+ }
+ nfsdstats.ra_size = i/sizeof(struct raparms);
+ memset(raparm_cache, 0, i);
+
+ i = HASHSIZE * sizeof (struct list_head);
+ while (1) {
+ hash_list = kmalloc (i, GFP_KERNEL);
+ if (!hash_list)
+ i /= 2;
+ else
+ break;
+ if (i == 0) {
+ kfree(raparm_cache);
+ raparm_cache = NULL;
+ printk (KERN_ERR "nfsd: cannot allocate space for hash list in racache\n");
+ return -1;
+ }
+ }
+
+ for (i = 0, rahead = hash_list; i < HASHSIZE; i++, rahead++)
+ INIT_LIST_HEAD(rahead);
+ INIT_LIST_HEAD(&free_head);
+ for (i = 0, rp = raparm_cache; i < CACHESIZE; i++, rp++)
+ list_add(&rp->p_lru, &free_head);
+ INIT_LIST_HEAD(&lru_head);
+
+ racache_init = 1;
+ return 0;
+}
+
+void
+nfsd_racache_shutdown(void)
+{
+ if (!racache_init)
+ return;
+ kfree (raparm_cache);
+ raparm_cache = NULL;
+ kfree (hash_list);
+ hash_list = NULL;
+ racache_init = 0;
+}
+
+/* Insert a new entry into the hash table. */
+static inline struct raparms *
+nfsd_racache_insert(ino_t ino, dev_t dev)
+{
+ struct raparms *ra = NULL;
+ struct list_head *rap;
+
+ if (list_empty(&free_head)) {
+ /* Replace with LRU. */
+ struct raparms *prev, *next;
+ ra = list_entry(lru_head.prev, struct raparms, p_lru);
+ list_del(&ra->p_hash);
+ list_del(lru_head.prev);
+ } else {
+ ra = list_entry(free_head.next, struct raparms, p_lru);
+ list_del(free_head.next);
+ }
+
+ memset(ra, 0, sizeof(*ra));
+ ra->p_dev = dev;
+ ra->p_ino = ino;
+ rap = (struct list_head *) &hash_list[REQHASH(ino, dev)];
+ list_add(&ra->p_hash, rap);
+ list_add(&ra->p_lru, &lru_head);
+ return ra;
+}
+
+/*
+ * Try to find an entry matching the current call in the cache. When none
+ * is found, we grab the oldest unlocked entry off the LRU list.
+ * Note that no operation within the loop may sleep.
+ */
+struct raparms *
+nfsd_get_raparms(dev_t dev, ino_t ino)
+{
+ struct raparms *rahead;
+ struct raparms *ra = NULL;
+ struct list_head *hlist;
+ struct list_head *tmp;
+
+ if (!racache_init)
+ return NULL;
+ spin_lock(&racache_lock);
+ hlist = &hash_list[REQHASH(ino, dev)];
+ list_for_each(tmp, hlist) {
+ ra = list_entry(tmp, struct raparms, p_hash);
+ if ((ra->p_ino == ino) && (ra->p_dev == dev)) {
+ /* Do LRU reordering */
+ list_del(&ra->p_lru);
+ list_add(&ra->p_lru, &lru_head);
+ nfsdstats.ra_hits++;
+ goto found;
+ }
+ }
+
+ /* Did not find one. Get a new item and insert it into the hash table. */
+ ra = nfsd_racache_insert(ino, dev);
+ nfsdstats.ra_misses++;
+found:
+ spin_unlock(&racache_lock);
+ return ra;
+}
-
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