Hey Tom-
On Tue, Aug 14, 2018 at 01:54:02PM -0500, Tom Zanussi wrote:
> v3.18.117-rt105 rt-stable review patch. If anyone has any objections,
> please let me know.
>
> ------------------
>
> From: Julia Cartwright <julia@xxxxxx>
>
> [ Upstream rt-devel commit c160736542d7b3d67da32848d2f028b8e35730e5 ]
>
> Currently, the squashfs multi_cpu decompressor makes use of
> get_cpu_ptr()/put_cpu_ptr(), which unconditionally disable preemption
> during decompression.
>
> Because the workload is distributed across CPUs, all CPUs can observe a
> very high wakeup latency, which has been seen to be as much as 8000us.
>
> Convert this decompressor to make use of a local lock, which will allow
> execution of the decompressor with preemption-enabled, but also ensure
> concurrent accesses to the percpu compressor data on the local CPU will
> be serialized.
>
> Cc: stable-rt@xxxxxxxxxxxxxxx
> Reported-by: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxxxxxxxx>
> Tested-by: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Julia Cartwright <julia@xxxxxx>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
> ---
[..]
> void *squashfs_decompressor_create(struct squashfs_sb_info *msblk,
> void *comp_opts)
> {
> @@ -79,10 +82,15 @@ int squashfs_decompress(struct squashfs_sb_info *msblk, struct buffer_head **bh,
> {
> 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;
> +
> + stream = get_locked_ptr(stream_lock, percpu);
This patch depends on the introduction of the {get,put}_locked_ptr()
per-cpu access variants. So, you'll want to also pull commit
3d45cf23db4f76cd3 ("locallock: provide {get,put}_locked_ptr() variants")
>From rt-devel as well.
Julia
