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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 Diff line number Diff line
@@ -25,6 +25,50 @@ config SQUASHFS 


	  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

	bool "Squashfs XATTR support"

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


	  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

	bool "Include support for XZ compressed file systems"

	depends on SQUASHFS

fs/squashfs/Makefile

+3 −7
Original line number Diff line number Diff line
@@ -5,14 +5,10 @@ 
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 += 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_LZO) += lzo_wrapper.o

squashfs-$(CONFIG_SQUASHFS_XZ) += xz_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 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();

}