On Wed, Nov 20, 2013 at 01:48:06AM +0000, Phillip Lougher wrote:
> 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.
>
> V2:
> * squashfs_decompressor_create: improve error handling path, re freeing
> of decompressors and comp_opts
> * decompressor_multi_percpu.c: include percpu.h header
> * Kconfig: indentation
>
> Signed-off-by: Phillip Lougher <phil...@squashfs.org.uk>
> ---
> fs/squashfs/Kconfig | 57 ++++++++++++++-----
> fs/squashfs/Makefile | 10 +---
> fs/squashfs/decompressor_multi_percpu.c | 98
> +++++++++++++++++++++++++++++++++
> 3 files changed, 145 insertions(+), 20 deletions(-)
> create mode 100644 fs/squashfs/decompressor_multi_percpu.c
>
> diff --git a/fs/squashfs/Kconfig b/fs/squashfs/Kconfig
> index 1c6d340..159bd66 100644
> --- a/fs/squashfs/Kconfig
> +++ b/fs/squashfs/Kconfig
> @@ -25,6 +25,50 @@ config SQUASHFS
>
> If unsure, say N.
>
> +choice
> + prompt "Decompressor parallelisation options"
Nitpick:
How about adding default explicitly?
default SQUASHFS_DECOMP_SINGLE
> + 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
Minor:
^
unnecessary white space.
> + decompression is load-balanced across the cores.
Actually, I am not sure it's good idea to mention percpu in description.
Normal people wouldn't know that and I think what they can want to know
is what's benefit compared to SQUASHFS_DECOMP_MULTI.
How about this?
This decompressor implementation uses a maximum of one
decompressor per core and the decompressor is allocated
statically so memory footprint is small and limited
and I/O cannot be fluctuated by not failing decompressor
dynamic allocation compared to SQUAHSDS_DECOMP_MULTI.
And I'd like to see what's your point about "decompression is load-balanced
across the cores".
If scheduler assigns process A, B, C into a core, it couldn't be load-balanced.
If scheduler assign process A, B, C into each core, it could be load-balanced.
And it's same with SQUSHFS_DECOMP_MULTI.
Could you elaborate it a bit?
Otherwise, looks good to me.
Thanks!
> +
> +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 dfebc3b..5833b96 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 0000000..0e7b679
> --- /dev/null
> +++ b/fs/squashfs/decompressor_multi_percpu.c
> @@ -0,0 +1,98 @@
> +/*
> + * Copyright (c) 2013
> + * Phillip Lougher <phil...@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();
> +}
> --
> 1.8.3.2
>
> --
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--
Kind regards,
Minchan Kim
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