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Commit b7ce2277 authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Ingo Molnar
Browse files

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: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent e5925394

include/linux/init_task.h

+1 −1
Original line number Diff line number Diff line
@@ -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

include/linux/sched.h

+1 −1
Original line number Diff line number Diff line
@@ -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 */

kernel/fork.c

+1 −1
Original line number Diff line number Diff line
@@ -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

kernel/sched/cputime.c

+24 −22
Original line number Diff line number Diff line
@@ -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));

}