On 8/30/23 23:00, Bongkyu Kim wrote:
> Disable reader optimistic spinning by default. And, can enable it
> by "rwsem.opt_rspin" cmdline.
>
> Also, fix compile error without CONFIG_RWSEM_SPIN_ON_OWNER (reported by
> kernel test robot)
>
> Reported-by: kernel test robot <[email protected]>
> Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
> Signed-off-by: Bongkyu Kim <[email protected]>
> ---
> .../admin-guide/kernel-parameters.txt | 9 +++++++++
> kernel/locking/rwsem.c | 18 +++++++++++++++++-
> 2 files changed, 26 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 772b54df084b..adf16a07fe4d 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5605,6 +5605,15 @@
>
> rw [KNL] Mount root device read-write on boot
>
> + rwsem.opt_rspin [KNL]
> + Use rwsem reader optimistic spinning. Reader optimistic
> + spinning is helpful when the reader critical section is
> + short and there aren't that many readers around.
> + For example, enable this option may improve performance
> + in mobile workload that there're not many readers, but
> + may reduce performance in server workload that there're
> + many readers.
> +
> S [KNL] Run init in single mode
>
> s390_iommu= [HW,S390]
> diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
> index 9c0462d515c1..de3f173d94d4 100644
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -117,6 +117,19 @@
> # define DEBUG_RWSEMS_WARN_ON(c, sem)
> #endif
>
> +#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
> +static bool rwsem_opt_rspin;
You need to move this definition out of the "ifdef
CONFIG_RWSEM_SPIN_ON_OWNER" block or a compilation error in
rwsem_down_read_slowpath() may happen if CONFIG_RWSEM_SPIN_ON_OWNER
isn't defined. You may also add __ro_after_init to rwsem_opt_rspin.
Cheers,
Longman
> +
> +static int __init opt_rspin(char *str)
> +{
> + rwsem_opt_rspin = true;
> +
> + return 0;
> +}
> +
> +early_param("rwsem.opt_rspin", opt_rspin);
> +#endif
> +
> /*
> * On 64-bit architectures, the bit definitions of the count are:
> *
> @@ -1083,7 +1096,7 @@ static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
> return false;
> }
>
> -static inline bool rwsem_no_spinners(sem)
> +static inline bool rwsem_no_spinners(struct rw_semaphore *sem)
> {
> return false;
> }
> @@ -1157,6 +1170,9 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int stat
> return sem;
> }
>
> + if (!IS_ENABLED(CONFIG_RWSEM_SPIN_ON_OWNER) || !rwsem_opt_rspin)
> + goto queue;
> +
> /*
> * Save the current read-owner of rwsem, if available, and the
> * reader nonspinnable bit.