sched/cputime: Convert vtime_seqlock to seqcount

The cputime can only be updated by the current task itself, even in
vtime case. So we can safely use seqcount instead of seqlock as there
is no writer concurrency involved.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E . McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1447948054-28668-8-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 1c1ff7e4faa4bf158166b789605107f6a65baf44..f2cb8d45513d182bef20020c775c617f8215af3a 100644 (file)
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -150,7 +150,7 @@ extern struct task_group root_task_group;
 
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
 # define INIT_VTIME(tsk)                                               \
-       .vtime_seqlock = __SEQLOCK_UNLOCKED(tsk.vtime_seqlock), \
+       .vtime_seqcount = SEQCNT_ZERO(tsk.vtime_seqcount),      \
        .vtime_snap = 0,                                \
        .vtime_snap_whence = VTIME_SYS,
 #else

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3533168fe7d1f188b0360e59e8baa5ba49bafab8..3b0de68bce41e8d8cb3e65df082aeda436e63030 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1519,7 +1519,7 @@ struct task_struct {
        cputime_t gtime;
        struct prev_cputime prev_cputime;
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
-       seqlock_t vtime_seqlock;
+       seqcount_t vtime_seqcount;
        unsigned long long vtime_snap;
        enum {
                /* Task is sleeping or running in a CPU with VTIME inactive */

diff --git a/kernel/fork.c b/kernel/fork.c
index c0a13706b1a75f09c47f8d86d0a1f2d80d5c8d11..eea32b55432a031dd68416e3fd7edc28fa4246af 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1348,7 +1348,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
        prev_cputime_init(&p->prev_cputime);
 
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
-       seqlock_init(&p->vtime_seqlock);
+       seqcount_init(&p->vtime_seqcount);
        p->vtime_snap = 0;
        p->vtime_snap_whence = VTIME_INACTIVE;
 #endif

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 9989c3f6172370916b7d062741f9b363fc1240dd..d5ff5c6bf829ad7ee2549c90d2c178e9b71ab344 100644 (file)
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -696,37 +696,37 @@ static void __vtime_account_system(struct task_struct *tsk)
 
 void vtime_account_system(struct task_struct *tsk)
 {
-       write_seqlock(&tsk->vtime_seqlock);
+       write_seqcount_begin(&tsk->vtime_seqcount);
        __vtime_account_system(tsk);
-       write_sequnlock(&tsk->vtime_seqlock);
+       write_seqcount_end(&tsk->vtime_seqcount);
 }
 
 void vtime_gen_account_irq_exit(struct task_struct *tsk)
 {
-       write_seqlock(&tsk->vtime_seqlock);
+       write_seqcount_begin(&tsk->vtime_seqcount);
        __vtime_account_system(tsk);
        if (context_tracking_in_user())
                tsk->vtime_snap_whence = VTIME_USER;
-       write_sequnlock(&tsk->vtime_seqlock);
+       write_seqcount_end(&tsk->vtime_seqcount);
 }
 
 void vtime_account_user(struct task_struct *tsk)
 {
        cputime_t delta_cpu;
 
-       write_seqlock(&tsk->vtime_seqlock);
+       write_seqcount_begin(&tsk->vtime_seqcount);
        delta_cpu = get_vtime_delta(tsk);
        tsk->vtime_snap_whence = VTIME_SYS;
        account_user_time(tsk, delta_cpu, cputime_to_scaled(delta_cpu));
-       write_sequnlock(&tsk->vtime_seqlock);
+       write_seqcount_end(&tsk->vtime_seqcount);
 }
 
 void vtime_user_enter(struct task_struct *tsk)
 {
-       write_seqlock(&tsk->vtime_seqlock);
+       write_seqcount_begin(&tsk->vtime_seqcount);
        __vtime_account_system(tsk);
        tsk->vtime_snap_whence = VTIME_USER;
-       write_sequnlock(&tsk->vtime_seqlock);
+       write_seqcount_end(&tsk->vtime_seqcount);
 }
 
 void vtime_guest_enter(struct task_struct *tsk)
@@ -738,19 +738,19 @@ void vtime_guest_enter(struct task_struct *tsk)
         * synchronization against the reader (task_gtime())
         * that can thus safely catch up with a tickless delta.
         */
-       write_seqlock(&tsk->vtime_seqlock);
+       write_seqcount_begin(&tsk->vtime_seqcount);
        __vtime_account_system(tsk);
        current->flags |= PF_VCPU;
-       write_sequnlock(&tsk->vtime_seqlock);
+       write_seqcount_end(&tsk->vtime_seqcount);
 }
 EXPORT_SYMBOL_GPL(vtime_guest_enter);
 
 void vtime_guest_exit(struct task_struct *tsk)
 {
-       write_seqlock(&tsk->vtime_seqlock);
+       write_seqcount_begin(&tsk->vtime_seqcount);
        __vtime_account_system(tsk);
        current->flags &= ~PF_VCPU;
-       write_sequnlock(&tsk->vtime_seqlock);
+       write_seqcount_end(&tsk->vtime_seqcount);
 }
 EXPORT_SYMBOL_GPL(vtime_guest_exit);
 
@@ -763,24 +763,26 @@ void vtime_account_idle(struct task_struct *tsk)
 
 void arch_vtime_task_switch(struct task_struct *prev)
 {
-       write_seqlock(&prev->vtime_seqlock);
+       write_seqcount_begin(&prev->vtime_seqcount);
        prev->vtime_snap_whence = VTIME_INACTIVE;
-       write_sequnlock(&prev->vtime_seqlock);
+       write_seqcount_end(&prev->vtime_seqcount);
 
-       write_seqlock(&current->vtime_seqlock);
+       write_seqcount_begin(&current->vtime_seqcount);
        current->vtime_snap_whence = VTIME_SYS;
        current->vtime_snap = sched_clock_cpu(smp_processor_id());
-       write_sequnlock(&current->vtime_seqlock);
+       write_seqcount_end(&current->vtime_seqcount);
 }
 
 void vtime_init_idle(struct task_struct *t, int cpu)
 {
        unsigned long flags;
 
-       write_seqlock_irqsave(&t->vtime_seqlock, flags);
+       local_irq_save(flags);
+       write_seqcount_begin(&t->vtime_seqcount);
        t->vtime_snap_whence = VTIME_SYS;
        t->vtime_snap = sched_clock_cpu(cpu);
-       write_sequnlock_irqrestore(&t->vtime_seqlock, flags);
+       write_seqcount_end(&t->vtime_seqcount);
+       local_irq_restore(flags);
 }
 
 cputime_t task_gtime(struct task_struct *t)
@@ -792,13 +794,13 @@ cputime_t task_gtime(struct task_struct *t)
                return t->gtime;
 
        do {
-               seq = read_seqbegin(&t->vtime_seqlock);
+               seq = read_seqcount_begin(&t->vtime_seqcount);
 
                gtime = t->gtime;
                if (t->vtime_snap_whence == VTIME_SYS && t->flags & PF_VCPU)
                        gtime += vtime_delta(t);
 
-       } while (read_seqretry(&t->vtime_seqlock, seq));
+       } while (read_seqcount_retry(&t->vtime_seqcount, seq));
 
        return gtime;
 }
@@ -821,7 +823,7 @@ fetch_task_cputime(struct task_struct *t,
                *udelta = 0;
                *sdelta = 0;
 
-               seq = read_seqbegin(&t->vtime_seqlock);
+               seq = read_seqcount_begin(&t->vtime_seqcount);
 
                if (u_dst)
                        *u_dst = *u_src;
@@ -845,7 +847,7 @@ fetch_task_cputime(struct task_struct *t,
                        if (t->vtime_snap_whence == VTIME_SYS)
                                *sdelta = delta;
                }
-       } while (read_seqretry(&t->vtime_seqlock, seq));
+       } while (read_seqcount_retry(&t->vtime_seqcount, seq));
 }