Messages in this thread Patch in this message | | | From | Sebastian Andrzej Siewior <> | Subject | [PATCH v2 4/7] squashfs: make use of local lock in multi_cpu decompressor | Date | Sun, 24 May 2020 23:57:36 +0200 |
| |
From: Julia Cartwright <julia@ni.com>
The squashfs multi CPU decompressor makes use of get_cpu_ptr() to acquire a pointer to per-CPU data. get_cpu_ptr() implicitly disables preemption which serializes the access to the per-CPU data.
But decompression can take quite some time depending on the size. The observed preempt disabled times in real world scenarios went up to 8ms, causing massive wakeup latencies. This happens on all CPUs as the decompression is fully parallelized.
Replace the implicit preemption control with an explicit local lock. This allows RT kernels to substitute it with a real per CPU lock, which serializes the access but keeps the code section preemptible. On non RT kernels this maps to preempt_disable() as before, i.e. no functional change.
[ bigeasy: Use local_lock(), patch description]
Cc: Phillip Lougher <phillip@squashfs.org.uk> Reported-by: Alexander Stein <alexander.stein@systec-electronic.com> Signed-off-by: Julia Cartwright <julia@ni.com> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Tested-by: Alexander Stein <alexander.stein@systec-electronic.com> --- fs/squashfs/decompressor_multi_percpu.c | 21 ++++++++++++++------- 1 file changed, 14 insertions(+), 7 deletions(-)
diff --git a/fs/squashfs/decompressor_multi_percpu.c b/fs/squashfs/decompressor_multi_percpu.c index 2a2a2d106440e..bac511cdebdb0 100644 --- a/fs/squashfs/decompressor_multi_percpu.c +++ b/fs/squashfs/decompressor_multi_percpu.c @@ -8,6 +8,7 @@ #include <linux/slab.h> #include <linux/percpu.h> #include <linux/buffer_head.h> +#include <linux/locallock.h> #include "squashfs_fs.h" #include "squashfs_fs_sb.h" @@ -20,7 +21,8 @@ */ struct squashfs_stream { - void *stream; + void *stream; + struct local_lock lock; }; void *squashfs_decompressor_create(struct squashfs_sb_info *msblk, @@ -41,6 +43,7 @@ void *squashfs_decompressor_create(struct squashfs_sb_info *msblk, err = PTR_ERR(stream->stream); goto out; } + local_lock_init(&stream->lock); } kfree(comp_opts); @@ -75,12 +78,16 @@ void squashfs_decompressor_destroy(struct squashfs_sb_info *msblk) int squashfs_decompress(struct squashfs_sb_info *msblk, struct buffer_head **bh, int b, int offset, int length, struct squashfs_page_actor *output) { - 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, bh, b, - offset, length, output); - put_cpu_ptr(stream); + struct squashfs_stream *stream; + int res; + + local_lock(&msblk->stream->lock); + stream = this_cpu_ptr(msblk->stream); + + res = msblk->decompressor->decompress(msblk, stream->stream, bh, b, + offset, length, output); + + local_unlock(&msblk->stream->lock); if (res < 0) ERROR("%s decompression failed, data probably corrupt\n", -- 2.27.0.rc0
| |