Messages in this thread | | | Date | Thu, 31 Aug 2023 11:22:50 -0400 | Subject | Re: [PATCH v1 2/2] locking/rwsem: Make reader optimistic spinning optional | From | Waiman Long <> |
| |
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 <lkp@intel.com> > Closes: https://lore.kernel.org/oe-kbuild-all/202306010043.VJHcuCnb-lkp@intel.com/ > Signed-off-by: Bongkyu Kim <bongkyu7.kim@samsung.com> > --- > .../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.
| |