* Suren Baghdasaryan <surenb@xxxxxxxxxx> [241121 11:28]:
> Add raw_seqcount_try_begin() to opens a read critical section of the given
> seqcount_t if the counter is even. This enables eliding the critical
> section entirely if the counter is odd, instead of doing the speculation
> knowing it will fail.
>
> Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> ---
> Applies over Linus' ToT
>
> include/linux/seqlock.h | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
> index 5298765d6ca4..22c2c48b4265 100644
> --- a/include/linux/seqlock.h
> +++ b/include/linux/seqlock.h
> @@ -318,6 +318,28 @@ SEQCOUNT_LOCKNAME(mutex, struct mutex, true, mutex)
> __seq; \
> })
>
> +/**
> + * raw_seqcount_try_begin() - begin a seqcount_t read critical section
> + * w/o lockdep and w/o counter stabilization
> + * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
> + *
> + * Similar to raw_seqcount_begin(), except it enables eliding the critical
> + * section entirely if odd, instead of doing the speculation knowing it will
> + * fail.
> + *
> + * Useful when counter stabilization is more or less equivalent to taking
> + * the lock and there is a slowpath that does that.
> + *
> + * If true, start will be set to the (even) sequence count read.
> + *
> + * Return: true when a read critical section is started.
> + */
> +#define raw_seqcount_try_begin(s, start) \
> +({ \
> + start = raw_read_seqcount(s); \
> + !(start & 1); \
> +})
> +
> /**
> * raw_seqcount_begin() - begin a seqcount_t read critical section w/o
> * lockdep and w/o counter stabilization
>
> base-commit: 43fb83c17ba2d63dfb798f0be7453ed55ca3f9c2
> --
> 2.47.0.338.g60cca15819-goog
>
