Commit d208383d authored by Phillip Lougher's avatar Phillip Lougher
Browse files

Squashfs: add multi-threaded decompression using percpu variable 



Add a multi-threaded decompression implementation which uses
percpu variables.

Using percpu variables has advantages and disadvantages over
implementations which do not use percpu variables.

Advantages:
  * the nature of percpu variables ensures decompression is
    load-balanced across the multiple cores.
  * simplicity.

Disadvantages: it limits decompression to one thread per core.

Signed-off-by: default avatarPhillip Lougher <phillip@squashfs.org.uk>
parent cd59c2ec

fs/squashfs/Kconfig

+44 −13
Original line number Original line Diff line number Diff line
@@ -25,6 +25,50 @@ config SQUASHFS 




	  If unsure, say N.

	  If unsure, say N.





choice

	prompt "Decompressor parallelisation options"

	depends on SQUASHFS

	help

	  Squashfs now supports three parallelisation options for

	  decompression.  Each one exhibits various trade-offs between

	  decompression performance and CPU and memory usage.



	  If in doubt, select "Single threaded compression"



config SQUASHFS_DECOMP_SINGLE

	bool "Single threaded compression"

	help

	  Traditionally Squashfs has used single-threaded decompression.

	  Only one block (data or metadata) can be decompressed at any

	  one time.  This limits CPU and memory usage to a minimum.



config SQUASHFS_DECOMP_MULTI

	bool "Use multiple decompressors for parallel I/O"

	help

	  By default Squashfs uses a single decompressor but it gives

	  poor performance on parallel I/O workloads when using multiple CPU

	  machines due to waiting on decompressor availability.



	  If you have a parallel I/O workload and your system has enough memory,

	  using this option may improve overall I/O performance.



	  This decompressor implementation uses up to two parallel

	  decompressors per core.  It dynamically allocates decompressors

	  on a demand basis.



config SQUASHFS_DECOMP_MULTI_PERCPU

	bool "Use percpu multiple decompressors for parallel I/O"

	help

	  By default Squashfs uses a single decompressor but it gives

	  poor performance on parallel I/O workloads when using multiple CPU

	  machines due to waiting on decompressor availability.



	  This decompressor implementation uses a maximum of one

	  decompressor per core.  It uses percpu variables to ensure

	  decompression is load-balanced across the cores.



endchoice



config SQUASHFS_XATTR

config SQUASHFS_XATTR

	bool "Squashfs XATTR support"

	bool "Squashfs XATTR support"

	depends on SQUASHFS

	depends on SQUASHFS
@@ -63,19 +107,6 @@ config SQUASHFS_LZO 




	  If unsure, say N.

	  If unsure, say N.





config SQUASHFS_MULTI_DECOMPRESSOR

	bool "Use multiple decompressors for handling parallel I/O"

	depends on SQUASHFS

	help

	  By default Squashfs uses a single decompressor but it gives

	  poor performance on parallel I/O workloads when using multiple CPU

	  machines due to waiting on decompressor availability.



	  If you have a parallel I/O workload and your system has enough memory,

	  using this option may improve overall I/O performance.



	  If unsure, say N.



config SQUASHFS_XZ

config SQUASHFS_XZ

	bool "Include support for XZ compressed file systems"

	bool "Include support for XZ compressed file systems"

	depends on SQUASHFS

	depends on SQUASHFS

fs/squashfs/Makefile

+3 −7
Original line number Original line Diff line number Diff line
@@ -5,14 +5,10 @@ 
obj-$(CONFIG_SQUASHFS) += squashfs.o

obj-$(CONFIG_SQUASHFS) += squashfs.o

squashfs-y += block.o cache.o dir.o export.o file.o fragment.o id.o inode.o

squashfs-y += block.o cache.o dir.o export.o file.o fragment.o id.o inode.o

squashfs-y += namei.o super.o symlink.o decompressor.o

squashfs-y += namei.o super.o symlink.o decompressor.o



squashfs-$(CONFIG_SQUASHFS_DECOMP_SINGLE) += decompressor_single.o

squashfs-$(CONFIG_SQUASHFS_DECOMP_MULTI) += decompressor_multi.o

squashfs-$(CONFIG_SQUASHFS_DECOMP_MULTI_PERCPU) += decompressor_multi_percpu.o

squashfs-$(CONFIG_SQUASHFS_XATTR) += xattr.o xattr_id.o

squashfs-$(CONFIG_SQUASHFS_XATTR) += xattr.o xattr_id.o

squashfs-$(CONFIG_SQUASHFS_LZO) += lzo_wrapper.o

squashfs-$(CONFIG_SQUASHFS_LZO) += lzo_wrapper.o

squashfs-$(CONFIG_SQUASHFS_XZ) += xz_wrapper.o

squashfs-$(CONFIG_SQUASHFS_XZ) += xz_wrapper.o

squashfs-$(CONFIG_SQUASHFS_ZLIB) += zlib_wrapper.o
 
squashfs-$(CONFIG_SQUASHFS_ZLIB) += zlib_wrapper.o
 


ifdef CONFIG_SQUASHFS_MULTI_DECOMPRESSOR

	squashfs-y		+= decompressor_multi.o

else

	squashfs-y		+= decompressor_single.o

endif

fs/squashfs/decompressor_multi_percpu.c

0 → 100644
+98 −0
Original line number Original line Diff line number Diff line 
/*

 * Copyright (c) 2013

 * Phillip Lougher <phillip@squashfs.org.uk>

 *

 * This work is licensed under the terms of the GNU GPL, version 2. See

 * the COPYING file in the top-level directory.

 */



#include <linux/types.h>

#include <linux/slab.h>

#include <linux/percpu.h>

#include <linux/buffer_head.h>



#include "squashfs_fs.h"

#include "squashfs_fs_sb.h"

#include "decompressor.h"

#include "squashfs.h"



/*

 * This file implements multi-threaded decompression using percpu

 * variables, one thread per cpu core.

 */



struct squashfs_stream {

	void		*stream;

};



void *squashfs_decompressor_create(struct squashfs_sb_info *msblk,

						void *comp_opts)

{

	struct squashfs_stream *stream;

	struct squashfs_stream __percpu *percpu;

	int err, cpu;



	percpu = alloc_percpu(struct squashfs_stream);

	if (percpu == NULL)

		return ERR_PTR(-ENOMEM);



	for_each_possible_cpu(cpu) {

		stream = per_cpu_ptr(percpu, cpu);

		stream->stream = msblk->decompressor->init(msblk, comp_opts);

		if (IS_ERR(stream->stream)) {

			err = PTR_ERR(stream->stream);

			goto out;

		}

	}



	kfree(comp_opts);

	return (__force void *) percpu;



out:

	for_each_possible_cpu(cpu) {

		stream = per_cpu_ptr(percpu, cpu);

		if (!IS_ERR_OR_NULL(stream->stream))

			msblk->decompressor->free(stream->stream);

	}

	free_percpu(percpu);

	return ERR_PTR(err);

}



void squashfs_decompressor_destroy(struct squashfs_sb_info *msblk)

{

	struct squashfs_stream __percpu *percpu =

			(struct squashfs_stream __percpu *) msblk->stream;

	struct squashfs_stream *stream;

	int cpu;



	if (msblk->stream) {

		for_each_possible_cpu(cpu) {

			stream = per_cpu_ptr(percpu, cpu);

			msblk->decompressor->free(stream->stream);

		}

		free_percpu(percpu);

	}

}



int squashfs_decompress(struct squashfs_sb_info *msblk,

	void **buffer, struct buffer_head **bh, int b, int offset, int length,

	int srclength, int pages)

{

	struct squashfs_stream __percpu *percpu =

			(struct squashfs_stream __percpu *) msblk->stream;

	struct squashfs_stream *stream = get_cpu_ptr(percpu);

	int res = msblk->decompressor->decompress(msblk, stream->stream, buffer,

		bh, b, offset, length, srclength, pages);

	put_cpu_ptr(stream);



	if (res < 0)

		ERROR("%s decompression failed, data probably corrupt\n",

			msblk->decompressor->name);



	return res;

}



int squashfs_max_decompressors(void)

{

	return num_possible_cpus();

}

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