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sched/cputime: Convert vtime_seqlock to seqcount

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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>
This commit is contained in:
Frederic Weisbecker 2015-11-19 16:47:34 +01:00 committed by Ingo Molnar
parent e592539466
commit b7ce2277f0
4 changed files with 27 additions and 25 deletions
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2
include/linux/init_task.h
View File

@ -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

2
include/linux/sched.h
View File

@ -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 */

2
kernel/fork.c
View File

@ -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

46
kernel/sched/cputime.c
View File

@ -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));
}