Messages in this thread | | | Date | Fri, 20 Jan 2023 21:14:43 -0500 | Subject | Re: [PATCH] sched: Store restrict_cpus_allowed_ptr() call state | From | Waiman Long <> |
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On 1/20/23 16:08, Waiman Long wrote: > The user_cpus_ptr field was originally added by commit b90ca8badbd1 > ("sched: Introduce task_struct::user_cpus_ptr to track requested > affinity"). It was used only by arm64 arch due to possible asymmetric > CPU setup. > > Since commit 8f9ea86fdf99 ("sched: Always preserve the user requested > cpumask"), task_struct::user_cpus_ptr is repurposed to store user > requested cpu affinity specified in the sched_setaffinity(). > > This results in a performance regression in an arm64 system when booted > with "allow_mismatched_32bit_el0" on the command-line. The arch code will > (amongst other things) calls force_compatible_cpus_allowed_ptr() and > relax_compatible_cpus_allowed_ptr() when exec()'ing a 32-bit or a 64-bit > task respectively. Now a call to relax_compatible_cpus_allowed_ptr() > will always result in a __sched_setaffinity() call whether there is a > previous force_compatible_cpus_allowed_ptr() call or not. > > In order to fix this regression, a new scheduler flag > task_struct::cpus_allowed_restricted is now added to track if > force_compatible_cpus_allowed_ptr() has been called before or not. This > patch also updates the comments in force_compatible_cpus_allowed_ptr() > and relax_compatible_cpus_allowed_ptr() and handles their interaction > with sched_setaffinity(). > > Fixes: 8f9ea86fdf99 ("sched: Always preserve the user requested cpumask") > Reported-by: Will Deacon <will@kernel.org> > Signed-off-by: Waiman Long <longman@redhat.com> > --- > include/linux/sched.h | 3 +++ > kernel/sched/core.c | 55 ++++++++++++++++++++++++++++++++++++------- > kernel/sched/sched.h | 2 ++ > 3 files changed, 51 insertions(+), 9 deletions(-) > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index 853d08f7562b..f93f62a1f858 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -886,6 +886,9 @@ struct task_struct { > unsigned sched_contributes_to_load:1; > unsigned sched_migrated:1; > > + /* restrict_cpus_allowed_ptr() bit, serialized by scheduler locks */ > + unsigned cpus_allowed_restricted:1; > + > /* Force alignment to the next boundary: */ > unsigned :0; > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index bb1ee6d7bdde..c334c1971e81 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2999,15 +2999,49 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, > struct rq *rq; > > rq = task_rq_lock(p, &rf); > + > + if (ctx->flags & (SCA_CLR_RESTRICT | SCA_SET_RESTRICT)) { > + p->cpus_allowed_restricted = 0; > + } else if (p->cpus_allowed_restricted) { > + /* > + * If force_compatible_cpus_allowed_ptr() has been called, > + * we can't extend cpumask to beyond what is in cpus_mask. > + */ > + if (!cpumask_and(rq->scratch_mask, ctx->new_mask, > + &p->cpus_mask)) { > + task_rq_unlock(rq, p, &rf); > + return -EINVAL; > + } > + > + /* > + * In the unlikely event that sched_setaffinity() has been > + * called on a cpu with cpus_allowed_restricted flag set, > + * we have to store in user_cpus_ptr a restricted version > + * of cpu affinity mask that won't be restored when > + * relax_compatible_cpus_allowed_ptr() is called. > + * > + * Note that we don't need to do further user_cpus_ptr > + * masking below as cpus_mask should be a subset of > + * user_cpus_ptr if set. > + */ > + if (ctx->flags & SCA_USER) > + cpumask_copy((struct cpumask *)ctx->new_mask, rq->scratch_mask);
Sorry, that part is wrong. I forgot there were two masks in ctx. Will send out a v2.
Cheers, Longman
> + else > + ctx->new_mask = rq->scratch_mask; > + } > + > /* > * Masking should be skipped if SCA_USER or any of the SCA_MIGRATE_* > - * flags are set. > + * flags are set or when cpus_allowed_restricted flag has been set. > */ > - if (p->user_cpus_ptr && > + if (p->user_cpus_ptr && !p->cpus_allowed_restricted && > !(ctx->flags & (SCA_USER | SCA_MIGRATE_ENABLE | SCA_MIGRATE_DISABLE)) && > cpumask_and(rq->scratch_mask, ctx->new_mask, p->user_cpus_ptr)) > ctx->new_mask = rq->scratch_mask; > > + if (ctx->flags & SCA_SET_RESTRICT) > + p->cpus_allowed_restricted = 1; > + > return __set_cpus_allowed_ptr_locked(p, ctx, rq, &rf); > } > > @@ -3025,8 +3059,8 @@ EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr); > /* > * Change a given task's CPU affinity to the intersection of its current > * affinity mask and @subset_mask, writing the resulting mask to @new_mask. > - * If user_cpus_ptr is defined, use it as the basis for restricting CPU > - * affinity or use cpu_online_mask instead. > + * The cpus_allowed_restricted bit is set to indicate to a later > + * relax_compatible_cpus_allowed_ptr() call to relax the cpumask. > * > * If the resulting mask is empty, leave the affinity unchanged and return > * -EINVAL. > @@ -3037,7 +3071,7 @@ static int restrict_cpus_allowed_ptr(struct task_struct *p, > { > struct affinity_context ac = { > .new_mask = new_mask, > - .flags = 0, > + .flags = SCA_SET_RESTRICT, > }; > struct rq_flags rf; > struct rq *rq; > @@ -3069,9 +3103,8 @@ static int restrict_cpus_allowed_ptr(struct task_struct *p, > > /* > * Restrict the CPU affinity of task @p so that it is a subset of > - * task_cpu_possible_mask() and point @p->user_cpus_ptr to a copy of the > - * old affinity mask. If the resulting mask is empty, we warn and walk > - * up the cpuset hierarchy until we find a suitable mask. > + * task_cpu_possible_mask(). If the resulting mask is empty, we warn > + * and walk up the cpuset hierarchy until we find a suitable mask. > */ > void force_compatible_cpus_allowed_ptr(struct task_struct *p) > { > @@ -3126,10 +3159,14 @@ void relax_compatible_cpus_allowed_ptr(struct task_struct *p) > { > struct affinity_context ac = { > .new_mask = task_user_cpus(p), > - .flags = 0, > + .flags = SCA_CLR_RESTRICT, > }; > int ret; > > + /* Return if no previous force_compatible_cpus_allowed_ptr() call */ > + if (!data_race(p->cpus_allowed_restricted)) > + return; > + > /* > * Try to restore the old affinity mask with __sched_setaffinity(). > * Cpuset masking will be done there too. > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 771f8ddb7053..adcef29d5479 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -2293,6 +2293,8 @@ extern struct task_struct *pick_next_task_idle(struct rq *rq); > #define SCA_MIGRATE_DISABLE 0x02 > #define SCA_MIGRATE_ENABLE 0x04 > #define SCA_USER 0x08 > +#define SCA_CLR_RESTRICT 0x10 > +#define SCA_SET_RESTRICT 0x20 > > #ifdef CONFIG_SMP >
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