sched/vtime: Record CPU under seqcount for kcpustat needs

In order to compute the kcpustat delta on a nohz CPU, we'll need to
fetch the task running on that target. Checking that its vtime
state snapshot actually refers to the relevant target involves recording
that CPU under the seqcount locked on task switch.

This is a step toward making kcpustat moving forward on full nohz CPUs.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J . Wysocki <rjw@rjwysocki.net>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Link: https://lkml.kernel.org/r/20191016025700.31277-2-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2c2e56bd8913250e88982ee8e47e36b23081fe23..d5d07335a97b9ff69fd476a18e7e5c09e2df8861 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -259,6 +259,7 @@ struct vtime {
        seqcount_t              seqcount;
        unsigned long long      starttime;
        enum vtime_state        state;
+       unsigned int            cpu;
        u64                     utime;
        u64                     stime;
        u64                     gtime;

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index cef23c211f419c95fd78acb36ae0619d9254601f..40f58169225488424c9e6914e14f8a330fd22f5c 100644 (file)
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -818,6 +818,7 @@ void vtime_task_switch_generic(struct task_struct *prev)
        else
                __vtime_account_kernel(prev, vtime);
        vtime->state = VTIME_INACTIVE;
+       vtime->cpu = -1;
        write_seqcount_end(&vtime->seqcount);
 
        vtime = &current->vtime;
@@ -825,6 +826,7 @@ void vtime_task_switch_generic(struct task_struct *prev)
        write_seqcount_begin(&vtime->seqcount);
        vtime->state = VTIME_SYS;
        vtime->starttime = sched_clock();
+       vtime->cpu = smp_processor_id();
        write_seqcount_end(&vtime->seqcount);
 }
 
@@ -837,6 +839,7 @@ void vtime_init_idle(struct task_struct *t, int cpu)
        write_seqcount_begin(&vtime->seqcount);
        vtime->state = VTIME_SYS;
        vtime->starttime = sched_clock();
+       vtime->cpu = cpu;
        write_seqcount_end(&vtime->seqcount);
        local_irq_restore(flags);
 }