On Sun, Apr 13, 2025 at 11:00:52PM -0700, Boqun Feng wrote: > Add a module parameter for shazptr to allow skip the self scan in > synchronize_shaptr(). This can force every synchronize_shaptr() to use > shazptr scan kthread, and help testing the shazptr scan kthread. > > Another reason users may want to set this paramter is to reduce the self > scan CPU cost in synchronize_shaptr(). > > Signed-off-by: Boqun Feng <[email protected]>
One nit below, but nevertheless: Reviewed-by: Paul E. McKenney <[email protected]> > --- > kernel/locking/shazptr.c | 28 +++++++++++++++++++++------- > 1 file changed, 21 insertions(+), 7 deletions(-) > > diff --git a/kernel/locking/shazptr.c b/kernel/locking/shazptr.c > index a8559cb559f8..b3f7e8390eb2 100644 > --- a/kernel/locking/shazptr.c > +++ b/kernel/locking/shazptr.c > @@ -14,11 +14,17 @@ > #include <linux/completion.h> > #include <linux/kthread.h> > #include <linux/list.h> > +#include <linux/moduleparam.h> > #include <linux/mutex.h> > #include <linux/shazptr.h> > #include <linux/slab.h> > #include <linux/sort.h> > > +#ifdef MODULE_PARAM_PREFIX > +#undef MODULE_PARAM_PREFIX > +#endif > +#define MODULE_PARAM_PREFIX "shazptr." I do not believe that you need this when the desired MODULE_PARAM_PREFIX matches the name of the file, as it does in this case. For example, kernel/rcu/tree.c needs this to get the "rcutree." prefix, but kernel/rcu/refscale.c can do without it. > + > DEFINE_PER_CPU_SHARED_ALIGNED(void *, shazptr_slots); > EXPORT_PER_CPU_SYMBOL_GPL(shazptr_slots); > > @@ -252,6 +258,10 @@ static void synchronize_shazptr_busywait(void *ptr) > } > } > > +/* Disabled by default. */ > +static int skip_synchronize_self_scan; > +module_param(skip_synchronize_self_scan, int, 0644); > + > static void synchronize_shazptr_normal(void *ptr) > { > int cpu; > @@ -259,15 +269,19 @@ static void synchronize_shazptr_normal(void *ptr) > > smp_mb(); /* Synchronize with the smp_mb() in shazptr_acquire(). */ > > - for_each_possible_cpu(cpu) { > - void **slot = per_cpu_ptr(&shazptr_slots, cpu); > - void *val; > + if (unlikely(skip_synchronize_self_scan)) { > + blocking_grp_mask = ~0UL; > + } else { > + for_each_possible_cpu(cpu) { > + void **slot = per_cpu_ptr(&shazptr_slots, cpu); > + void *val; > > - /* Pair with smp_store_release() in shazptr_clear(). */ > - val = smp_load_acquire(slot); > + /* Pair with smp_store_release() in shazptr_clear(). */ > + val = smp_load_acquire(slot); > > - if (val == ptr || val == SHAZPTR_WILDCARD) > - blocking_grp_mask |= 1UL << (cpu / > shazptr_scan.cpu_grp_size); > + if (val == ptr || val == SHAZPTR_WILDCARD) > + blocking_grp_mask |= 1UL << (cpu / > shazptr_scan.cpu_grp_size); > + } > } > > /* Found blocking slots, prepare to wait. */ > -- > 2.47.1 >
