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>

1 files changed, 98 insertions, 0 deletions

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();
+}