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

3 files changed, 145 insertions, 20 deletions

diff --git a/fs/squashfs/Kconfig b/fs/squashfs/Kconfig
index 1c6d340fc61f..159bd6676dc2 100644
--- a/fs/squashfs/Kconfig
+++ b/fs/squashfs/Kconfig
@@ -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
diff --git a/fs/squashfs/Makefile b/fs/squashfs/Makefile
index dfebc3b12d61..5833b96ee69c 100644
--- a/fs/squashfs/Makefile
+++ b/fs/squashfs/Makefile
@@ -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
diff --git a/fs/squashfs/decompressor_multi_percpu.c b/fs/squashfs/decompressor_multi_percpu.c
new file mode 100644
index 000000000000..0e7b679bc4ad
--- /dev/null
+++ b/fs/squashfs/decompressor_multi_percpu.c
@@ -0,0 +1,98 @@
+/*
+ * 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();
+}