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Commit 3bd37062 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Ingo Molnar
Browse files

sched/core: Provide a pointer to the valid CPU mask 



In commit:

  4b53a341 ("sched/core: Remove the tsk_nr_cpus_allowed() wrapper")

the tsk_nr_cpus_allowed() wrapper was removed. There was not
much difference in !RT but in RT we used this to implement
migrate_disable(). Within a migrate_disable() section the CPU mask is
restricted to single CPU while the "normal" CPU mask remains untouched.

As an alternative implementation Ingo suggested to use:

	struct task_struct {
		const cpumask_t		*cpus_ptr;
		cpumask_t		cpus_mask;
        };
with
	t->cpus_ptr = &t->cpus_mask;

In -RT we then can switch the cpus_ptr to:

	t->cpus_ptr = &cpumask_of(task_cpu(p));

in a migration disabled region. The rules are simple:

 - Code that 'uses' ->cpus_allowed would use the pointer.
 - Code that 'modifies' ->cpus_allowed would use the direct mask.

Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190423142636.14347-1-bigeasy@linutronix.de


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent f2c7c76c

arch/ia64/kernel/mca.c

+1 −1
Original line number Diff line number Diff line
@@ -1831,7 +1831,7 @@ format_mca_init_stack(void *mca_data, unsigned long offset, 
	ti->cpu = cpu;

	p->stack = ti;

	p->state = TASK_UNINTERRUPTIBLE;

	cpumask_set_cpu(cpu, &p->cpus_allowed);

	cpumask_set_cpu(cpu, &p->cpus_mask);

	INIT_LIST_HEAD(&p->tasks);

	p->parent = p->real_parent = p->group_leader = p;

	INIT_LIST_HEAD(&p->children);

arch/mips/include/asm/switch_to.h

+2 −2
Original line number Diff line number Diff line
@@ -42,7 +42,7 @@ extern struct task_struct *ll_task; 
 * inline to try to keep the overhead down. If we have been forced to run on

 * a "CPU" with an FPU because of a previous high level of FP computation,

 * but did not actually use the FPU during the most recent time-slice (CU1

 * isn't set), we undo the restriction on cpus_allowed.

 * isn't set), we undo the restriction on cpus_mask.

 *

 * We're not calling set_cpus_allowed() here, because we have no need to

 * force prompt migration - we're already switching the current CPU to a
@@ -57,7 +57,7 @@ do { \ 
	    test_ti_thread_flag(__prev_ti, TIF_FPUBOUND) &&		\

	    (!(KSTK_STATUS(prev) & ST0_CU1))) {				\

		clear_ti_thread_flag(__prev_ti, TIF_FPUBOUND);		\

		prev->cpus_allowed = prev->thread.user_cpus_allowed;	\

		prev->cpus_mask = prev->thread.user_cpus_allowed;	\

	}								\

	next->thread.emulated_fp = 0;					\

} while(0)

arch/mips/kernel/mips-mt-fpaff.c

+1 −1
Original line number Diff line number Diff line
@@ -177,7 +177,7 @@ asmlinkage long mipsmt_sys_sched_getaffinity(pid_t pid, unsigned int len, 
	if (retval)

		goto out_unlock;



	cpumask_or(&allowed, &p->thread.user_cpus_allowed, &p->cpus_allowed);

	cpumask_or(&allowed, &p->thread.user_cpus_allowed, p->cpus_ptr);

	cpumask_and(&mask, &allowed, cpu_active_mask);



out_unlock:

arch/mips/kernel/traps.c

+3 −3
Original line number Diff line number Diff line
@@ -891,12 +891,12 @@ static void mt_ase_fp_affinity(void) 
		 * restricted the allowed set to exclude any CPUs with FPUs,

		 * we'll skip the procedure.

		 */

		if (cpumask_intersects(&current->cpus_allowed, &mt_fpu_cpumask)) {

		if (cpumask_intersects(&current->cpus_mask, &mt_fpu_cpumask)) {

			cpumask_t tmask;



			current->thread.user_cpus_allowed

				= current->cpus_allowed;

			cpumask_and(&tmask, &current->cpus_allowed,

				= current->cpus_mask;

			cpumask_and(&tmask, &current->cpus_mask,

				    &mt_fpu_cpumask);

			set_cpus_allowed_ptr(current, &tmask);

			set_thread_flag(TIF_FPUBOUND);

arch/powerpc/platforms/cell/spufs/sched.c

+1 −1
Original line number Diff line number Diff line
@@ -128,7 +128,7 @@ void __spu_update_sched_info(struct spu_context *ctx) 
	 * runqueue. The context will be rescheduled on the proper node

	 * if it is timesliced or preempted.

	 */

	cpumask_copy(&ctx->cpus_allowed, &current->cpus_allowed);

	cpumask_copy(&ctx->cpus_allowed, current->cpus_ptr);



	/* Save the current cpu id for spu interrupt routing. */

	ctx->last_ran = raw_smp_processor_id();