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Commit fce1456a authored by Greg Banks's avatar Greg Banks Committed by Linus Torvalds
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[PATCH] knfsd: make nfsd readahead params cache SMP-friendly 



Make the nfsd read-ahead params cache more SMP-friendly by changing the single
global list and lock into a fixed 16-bucket hashtable with per-bucket locks.
This reduces spinlock contention in nfsd_read() on read-heavy workloads on
multiprocessor servers.

Testing was on a 4 CPU 4 NIC Altix using 4 IRIX clients each doing 1K
streaming reads at full line rate.  The server had 128 nfsd threads, which
sizes the RA cache at 256 entries, of which only a handful were used.  Flat
profiling shows nfsd_read(), including the inlined nfsd_get_raparms(), taking
10.4% of each CPU.  This patch drops the contribution from nfsd() to 1.71% for
each CPU.

Signed-off-by: default avatarGreg Banks <gnb@melbourne.sgi.com>
Signed-off-by: default avatarNeil Brown <neilb@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 596bbe53

fs/nfsd/vfs.c

+44 −16
Original line number Diff line number Diff line
@@ -54,6 +54,7 @@ 
#include <linux/nfsd_idmap.h>

#include <linux/security.h>

#endif /* CONFIG_NFSD_V4 */

#include <linux/jhash.h>



#include <asm/uaccess.h>
@@ -81,10 +82,19 @@ struct raparms { 
	dev_t			p_dev;

	int			p_set;

	struct file_ra_state	p_ra;

	unsigned int		p_hindex;

};



struct raparm_hbucket {

	struct raparms		*pb_head;

	spinlock_t		pb_lock;

} ____cacheline_aligned_in_smp;



static struct raparms *		raparml;

static struct raparms *		raparm_cache;

#define RAPARM_HASH_BITS	4

#define RAPARM_HASH_SIZE	(1<<RAPARM_HASH_BITS)

#define RAPARM_HASH_MASK	(RAPARM_HASH_SIZE-1)

static struct raparm_hbucket	raparm_hash[RAPARM_HASH_SIZE];



/* 

 * Called from nfsd_lookup and encode_dirent. Check if we have crossed
@@ -743,16 +753,20 @@ nfsd_sync_dir(struct dentry *dp) 
 * Obtain the readahead parameters for the file

 * specified by (dev, ino).

 */

static DEFINE_SPINLOCK(ra_lock);



static inline struct raparms *

nfsd_get_raparms(dev_t dev, ino_t ino)

{

	struct raparms	*ra, **rap, **frap = NULL;

	int depth = 0;

	unsigned int hash;

	struct raparm_hbucket *rab;



	hash = jhash_2words(dev, ino, 0xfeedbeef) & RAPARM_HASH_MASK;

	rab = &raparm_hash[hash];



	spin_lock(&ra_lock);

	for (rap = &raparm_cache; (ra = *rap); rap = &ra->p_next) {

	spin_lock(&rab->pb_lock);

	for (rap = &rab->pb_head; (ra = *rap); rap = &ra->p_next) {

		if (ra->p_ino == ino && ra->p_dev == dev)

			goto found;

		depth++;
@@ -761,7 +775,7 @@ nfsd_get_raparms(dev_t dev, ino_t ino) 
	}

	depth = nfsdstats.ra_size*11/10;

	if (!frap) {	

		spin_unlock(&ra_lock);

		spin_unlock(&rab->pb_lock);

		return NULL;

	}

	rap = frap;
@@ -769,15 +783,16 @@ nfsd_get_raparms(dev_t dev, ino_t ino) 
	ra->p_dev = dev;

	ra->p_ino = ino;

	ra->p_set = 0;

	ra->p_hindex = hash;

found:

	if (rap != &raparm_cache) {

	if (rap != &rab->pb_head) {

		*rap = ra->p_next;

		ra->p_next   = raparm_cache;

		raparm_cache = ra;

		ra->p_next   = rab->pb_head;

		rab->pb_head = ra;

	}

	ra->p_count++;

	nfsdstats.ra_depth[depth*10/nfsdstats.ra_size]++;

	spin_unlock(&ra_lock);

	spin_unlock(&rab->pb_lock);

	return ra;

}
@@ -853,11 +868,12 @@ nfsd_vfs_read(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file, 


	/* Write back readahead params */

	if (ra) {

		spin_lock(&ra_lock);

		struct raparm_hbucket *rab = &raparm_hash[ra->p_hindex];

		spin_lock(&rab->pb_lock);

		ra->p_ra = file->f_ra;

		ra->p_set = 1;

		ra->p_count--;

		spin_unlock(&ra_lock);

		spin_unlock(&rab->pb_lock);

	}



	if (err >= 0) {
@@ -1833,11 +1849,11 @@ nfsd_permission(struct svc_export *exp, struct dentry *dentry, int acc) 
void

nfsd_racache_shutdown(void)

{

	if (!raparm_cache)

	if (!raparml)

		return;

	dprintk("nfsd: freeing readahead buffers.\n");

	kfree(raparml);

	raparm_cache = raparml = NULL;

	raparml = NULL;

}

/*

 * Initialize readahead param cache
@@ -1846,19 +1862,31 @@ int 
nfsd_racache_init(int cache_size)

{

	int	i;

	int	j = 0;

	int	nperbucket;



	if (raparm_cache)



	if (raparml)

		return 0;

	if (cache_size < 2*RAPARM_HASH_SIZE)

		cache_size = 2*RAPARM_HASH_SIZE;

	raparml = kmalloc(sizeof(struct raparms) * cache_size, GFP_KERNEL);



	if (raparml != NULL) {

		dprintk("nfsd: allocating %d readahead buffers.\n",

			cache_size);

		for (i = 0 ; i < RAPARM_HASH_SIZE ; i++) {

			raparm_hash[i].pb_head = NULL;

			spin_lock_init(&raparm_hash[i].pb_lock);

		}

		nperbucket = cache_size >> RAPARM_HASH_BITS;

		memset(raparml, 0, sizeof(struct raparms) * cache_size);

		for (i = 0; i < cache_size - 1; i++) {

			if (i % nperbucket == 0)

				raparm_hash[j++].pb_head = raparml + i;

			if (i % nperbucket < nperbucket-1)

				raparml[i].p_next = raparml + i + 1;

		}

		raparm_cache = raparml;

	} else {

		printk(KERN_WARNING

		       "nfsd: Could not allocate memory read-ahead cache.\n");