Messages in this thread | | | Date | Tue, 14 Apr 2020 12:19:56 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH 2/4] cpumask: Make cpumask_any() truly random |
| |
On Tue, 14 Apr 2020 16:05:54 +0100 Qais Yousef <qais.yousef@arm.com> wrote:
> Commit 46a87b3851f0 ("sched/core: Distribute tasks within affinity masks") > added a new cpumask_any_and_distribute() which truly returns a random > cpu within the mask. > > Previous patch renamed the function to cpumask_any_and(), so that old > users can take advantage of the new randomness behavior. > > Build up on that, and let cpumask_any() truly random too by re-using the > logic from cpumask_any_and(). > > Signed-off-by: Qais Yousef <qais.yousef@arm.com> > CC: Juri Lelli <juri.lelli@redhat.com> > CC: Vincent Guittot <vincent.guittot@linaro.org> > CC: Dietmar Eggemann <dietmar.eggemann@arm.com> > CC: Steven Rostedt <rostedt@goodmis.org> > CC: Ben Segall <bsegall@google.com> > CC: Mel Gorman <mgorman@suse.de> > CC: Andrew Morton <akpm@linux-foundation.org> > CC: Thomas Gleixner <tglx@linutronix.de> > CC: Yury Norov <yury.norov@gmail.com> > CC: Paul Turner <pjt@google.com> > CC: Alexey Dobriyan <adobriyan@gmail.com> > CC: Josh Don <joshdon@google.com> > CC: Pavan Kondeti <pkondeti@codeaurora.org> > CC: linux-kernel@vger.kernel.org > --- > include/linux/cpumask.h | 14 ++++++-------- > lib/cpumask.c | 24 ++++++++++++++++++++++++ > 2 files changed, 30 insertions(+), 8 deletions(-) > > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h > index e4d6d140a67c..7fb25d256043 100644 > --- a/include/linux/cpumask.h > +++ b/include/linux/cpumask.h > @@ -194,6 +194,11 @@ static inline unsigned int cpumask_local_spread(unsigned int i, int node) > return 0; > } > > +static inline int cpumask_any(const struct cpumask *src1p) > +{ > + return 0; > +} > + > static inline int cpumask_any_and(const struct cpumask *src1p, > const struct cpumask *src2p) > { > @@ -251,6 +256,7 @@ static inline unsigned int cpumask_next_zero(int n, const struct cpumask *srcp) > int cpumask_next_and(int n, const struct cpumask *, const struct cpumask *); > int cpumask_any_but(const struct cpumask *mask, unsigned int cpu); > unsigned int cpumask_local_spread(unsigned int i, int node); > +int cpumask_any(const struct cpumask *srcp); > int cpumask_any_and(const struct cpumask *src1p, const struct cpumask *src2p); > > /** > @@ -600,14 +606,6 @@ static inline void cpumask_copy(struct cpumask *dstp, > bitmap_copy(cpumask_bits(dstp), cpumask_bits(srcp), nr_cpumask_bits); > } > > -/** > - * cpumask_any - pick a "random" cpu from *srcp > - * @srcp: the input cpumask > - * > - * Returns >= nr_cpu_ids if no cpus set. > - */ > -#define cpumask_any(srcp) cpumask_first(srcp) > - > /** > * cpumask_first_and - return the first cpu from *srcp1 & *srcp2 > * @src1p: the first input > diff --git a/lib/cpumask.c b/lib/cpumask.c > index b527a153b023..bcac63e45374 100644 > --- a/lib/cpumask.c > +++ b/lib/cpumask.c > @@ -259,3 +259,27 @@ int cpumask_any_and(const struct cpumask *src1p, const struct cpumask *src2p) > return next; > } > EXPORT_SYMBOL(cpumask_any_and); > + > +/** > + * cpumask_any - pick a "random" cpu from *srcp > + * @srcp: the input cpumask > + * > + * Returns >= nr_cpu_ids if no cpus set. > + */ > +int cpumask_any(const struct cpumask *srcp) > +{ > + int next, prev; > + > + /* NOTE: our first selection will skip 0. */ > + prev = __this_cpu_read(distribute_cpu_mask_prev); > + > + next = cpumask_next(prev, srcp); > + if (next >= nr_cpu_ids) > + next = cpumask_first(srcp); > + > + if (next < nr_cpu_ids) > + __this_cpu_write(distribute_cpu_mask_prev, next);
Do we care if this gets preempted and migrated to a new CPU where we read "prev" from one distribute_cpu_mask_prev on one CPU and write it to another CPU?
-- Steve
> + > + return next; > +} > +EXPORT_SYMBOL(cpumask_any);
| |