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>
diff --git a/fs/squashfs/decompressor_multi_percpu.c b/fs/squashfs/decompressor_multi_percpu.c
new file mode 100644
index 0000000..0e7b679
--- /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();
+}