Commit 7394daa8 authored by David Howells's avatar David Howells
Browse files

FS-Cache: Add use of /proc and presentation of statistics 



Make FS-Cache create its /proc interface and present various statistical
information through it.  Also provide the functions for updating this
information.

These features are enabled by:

	CONFIG_FSCACHE_PROC
	CONFIG_FSCACHE_STATS
	CONFIG_FSCACHE_HISTOGRAM

The /proc directory for FS-Cache is also exported so that caching modules can
add their own statistics there too.

The FS-Cache module is loadable at this point, and the statistics files can be
examined by userspace:

	cat /proc/fs/fscache/stats
	cat /proc/fs/fscache/histogram

Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Acked-by: default avatarSteve Dickson <steved@redhat.com>
Acked-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Tested-by: default avatarDaire Byrne <Daire.Byrne@framestore.com>
parent 06b3db1b

Documentation/filesystems/caching/backend-api.txt

+0 −6
Original line number Diff line number Diff line
@@ -100,12 +100,6 @@ A sysfs directory called /sys/fs/fscache/<cachetag>/ is created if CONFIG_SYSFS 
is enabled.  This is accessible through the kobject struct fscache_cache::kobj

and is for use by the cache as it sees fit.



The cache driver may create itself a directory named for the cache type in the

/proc/fs/fscache/ directory.  This is available if CONFIG_FSCACHE_PROC is

enabled and is accessible through:



	struct proc_dir_entry *proc_fscache;





========================

RELEVANT DATA STRUCTURES

Documentation/filesystems/caching/fscache.txt

+5 −7
Original line number Diff line number Diff line
@@ -195,7 +195,6 @@ STATISTICAL INFORMATION 


If FS-Cache is compiled with the following options enabled:



	CONFIG_FSCACHE_PROC=y (implied by the following two)

	CONFIG_FSCACHE_STATS=y

	CONFIG_FSCACHE_HISTOGRAM=y
@@ -275,7 +274,7 @@ proc files. 
 (*) /proc/fs/fscache/histogram



	cat /proc/fs/fscache/histogram

	+HZ   +TIME OBJ INST  OP RUNS   OBJ RUNS  RETRV DLY RETRIEVLS

	JIFS  SECS  OBJ INST  OP RUNS   OBJ RUNS  RETRV DLY RETRIEVLS

	===== ===== ========= ========= ========= ========= =========



     This shows the breakdown of the number of times each amount of time
@@ -291,16 +290,16 @@ proc files. 
	RETRIEVLS	Time between beginning and end of a retrieval



     Each row shows the number of events that took a particular range of times.

     Each step is 1 jiffy in size.  The +HZ column indicates the particular

     jiffy range covered, and the +TIME field the equivalent number of seconds.

     Each step is 1 jiffy in size.  The JIFS column indicates the particular

     jiffy range covered, and the SECS field the equivalent number of seconds.





=========

DEBUGGING

=========



The FS-Cache facility can have runtime debugging enabled by adjusting the value

in:

If CONFIG_FSCACHE_DEBUG is enabled, the FS-Cache facility can have runtime

debugging enabled by adjusting the value in:



	/sys/module/fscache/parameters/debug
@@ -327,4 +326,3 @@ the control file. For example: 
	echo $((1|8|64)) >/sys/module/fscache/parameters/debug



will turn on all function entry debugging.

fs/fscache/Kconfig

+34 −0
Original line number Diff line number Diff line
@@ -11,6 +11,40 @@ config FSCACHE 


	  See Documentation/filesystems/caching/fscache.txt for more information.



config FSCACHE_STATS

	bool "Gather statistical information on local caching"

	depends on FSCACHE && PROC_FS

	help

	  This option causes statistical information to be gathered on local

	  caching and exported through file:



		/proc/fs/fscache/stats



	  The gathering of statistics adds a certain amount of overhead to

	  execution as there are a quite a few stats gathered, and on a

	  multi-CPU system these may be on cachelines that keep bouncing

	  between CPUs.  On the other hand, the stats are very useful for

	  debugging purposes.  Saying 'Y' here is recommended.



	  See Documentation/filesystems/caching/fscache.txt for more information.



config FSCACHE_HISTOGRAM

	bool "Gather latency information on local caching"

	depends on FSCACHE && PROC_FS

	help

	  This option causes latency information to be gathered on local

	  caching and exported through file:



		/proc/fs/fscache/histogram



	  The generation of this histogram adds a certain amount of overhead to

	  execution as there are a number of points at which data is gathered,

	  and on a multi-CPU system these may be on cachelines that keep

	  bouncing between CPUs.  On the other hand, the histogram may be

	  useful for debugging purposes.  Saying 'N' here is recommended.



	  See Documentation/filesystems/caching/fscache.txt for more information.



config FSCACHE_DEBUG

	bool "Debug FS-Cache"

	depends on FSCACHE

fs/fscache/Makefile

+4 −0
Original line number Diff line number Diff line
@@ -5,4 +5,8 @@ 
fscache-y := \

	main.o



fscache-$(CONFIG_PROC_FS) += proc.o

fscache-$(CONFIG_FSCACHE_STATS) += stats.o

fscache-$(CONFIG_FSCACHE_HISTOGRAM) += histogram.o



obj-$(CONFIG_FSCACHE) := fscache.o

fs/fscache/histogram.c

0 → 100644
+109 −0
Original line number Diff line number Diff line 
/* FS-Cache latency histogram

 *

 * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.

 * Written by David Howells (dhowells@redhat.com)

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public Licence

 * as published by the Free Software Foundation; either version

 * 2 of the Licence, or (at your option) any later version.

 */



#define FSCACHE_DEBUG_LEVEL THREAD

#include <linux/module.h>

#include <linux/proc_fs.h>

#include <linux/seq_file.h>

#include "internal.h"



atomic_t fscache_obj_instantiate_histogram[HZ];

atomic_t fscache_objs_histogram[HZ];

atomic_t fscache_ops_histogram[HZ];

atomic_t fscache_retrieval_delay_histogram[HZ];

atomic_t fscache_retrieval_histogram[HZ];



/*

 * display the time-taken histogram

 */

static int fscache_histogram_show(struct seq_file *m, void *v)

{

	unsigned long index;

	unsigned n[5], t;



	switch ((unsigned long) v) {

	case 1:

		seq_puts(m, "JIFS  SECS  OBJ INST  OP RUNS   OBJ RUNS "

			 " RETRV DLY RETRIEVLS\n");

		return 0;

	case 2:

		seq_puts(m, "===== ===== ========= ========= ========="

			 " ========= =========\n");

		return 0;

	default:

		index = (unsigned long) v - 3;

		n[0] = atomic_read(&fscache_obj_instantiate_histogram[index]);

		n[1] = atomic_read(&fscache_ops_histogram[index]);

		n[2] = atomic_read(&fscache_objs_histogram[index]);

		n[3] = atomic_read(&fscache_retrieval_delay_histogram[index]);

		n[4] = atomic_read(&fscache_retrieval_histogram[index]);

		if (!(n[0] | n[1] | n[2] | n[3] | n[4]))

			return 0;



		t = (index * 1000) / HZ;



		seq_printf(m, "%4lu  0.%03u %9u %9u %9u %9u %9u\n",

			   index, t, n[0], n[1], n[2], n[3], n[4]);

		return 0;

	}

}



/*

 * set up the iterator to start reading from the first line

 */

static void *fscache_histogram_start(struct seq_file *m, loff_t *_pos)

{

	if ((unsigned long long)*_pos >= HZ + 2)

		return NULL;

	if (*_pos == 0)

		*_pos = 1;

	return (void *)(unsigned long) *_pos;

}



/*

 * move to the next line

 */

static void *fscache_histogram_next(struct seq_file *m, void *v, loff_t *pos)

{

	(*pos)++;

	return (unsigned long long)*pos > HZ + 2 ?

		NULL : (void *)(unsigned long) *pos;

}



/*

 * clean up after reading

 */

static void fscache_histogram_stop(struct seq_file *m, void *v)

{

}



static const struct seq_operations fscache_histogram_ops = {

	.start		= fscache_histogram_start,

	.stop		= fscache_histogram_stop,

	.next		= fscache_histogram_next,

	.show		= fscache_histogram_show,

};



/*

 * open "/proc/fs/fscache/histogram" to provide latency data

 */

static int fscache_histogram_open(struct inode *inode, struct file *file)

{

	return seq_open(file, &fscache_histogram_ops);

}



const struct file_operations fscache_histogram_fops = {

	.owner		= THIS_MODULE,

	.open		= fscache_histogram_open,

	.read		= seq_read,

	.llseek		= seq_lseek,

	.release	= seq_release,

};

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