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Commit 031aeee0 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

srcu: Improve rcu_seq grace-period-counter abstraction 



The expedited grace-period code contains several open-coded shifts
know the format of an rcu_seq grace-period counter, which is not
particularly good style.  This commit therefore creates a new
rcu_seq_ctr() function that extracts the counter portion of the
counter, and an rcu_seq_state() function that extracts the low-order
state bit.  This commit prepares for SRCU callback parallelization,
which will require two state bits.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 91e27c35

kernel/rcu/rcu.h

+25 −4
Original line number Diff line number Diff line
@@ -61,20 +61,41 @@ 
 * Grace-period counter management.

 */



#define RCU_SEQ_CTR_SHIFT	1

#define RCU_SEQ_STATE_MASK	((1 << RCU_SEQ_CTR_SHIFT) - 1)



/*

 * Return the counter portion of a sequence number previously returned

 * by rcu_seq_snap() or rcu_seq_current().

 */

static inline unsigned long rcu_seq_ctr(unsigned long s)

{

	return s >> RCU_SEQ_CTR_SHIFT;

}



/*

 * Return the state portion of a sequence number previously returned

 * by rcu_seq_snap() or rcu_seq_current().

 */

static inline int rcu_seq_state(unsigned long s)

{

	return s & RCU_SEQ_STATE_MASK;

}



/* Adjust sequence number for start of update-side operation. */

static inline void rcu_seq_start(unsigned long *sp)

{

	WRITE_ONCE(*sp, *sp + 1);

	smp_mb(); /* Ensure update-side operation after counter increment. */

	WARN_ON_ONCE(!(*sp & 0x1));

	WARN_ON_ONCE(rcu_seq_state(*sp) != 1);

}



/* Adjust sequence number for end of update-side operation. */

static inline void rcu_seq_end(unsigned long *sp)

{

	smp_mb(); /* Ensure update-side operation before counter increment. */

	WARN_ON_ONCE(!(*sp & 0x1));

	WRITE_ONCE(*sp, *sp + 1);

	WARN_ON_ONCE(!rcu_seq_state(*sp));

	WRITE_ONCE(*sp, (*sp | RCU_SEQ_STATE_MASK) + 1);

}



/* Take a snapshot of the update side's sequence number. */
@@ -82,7 +103,7 @@ static inline unsigned long rcu_seq_snap(unsigned long *sp) 
{

	unsigned long s;



	s = (READ_ONCE(*sp) + 3) & ~0x1;

	s = (READ_ONCE(*sp) + 2 * RCU_SEQ_STATE_MASK + 1) & ~RCU_SEQ_STATE_MASK;

	smp_mb(); /* Above access must not bleed into critical section. */

	return s;

}

kernel/rcu/tree_exp.h

+4 −5
Original line number Diff line number Diff line
@@ -292,7 +292,7 @@ static bool exp_funnel_lock(struct rcu_state *rsp, unsigned long s) 
			trace_rcu_exp_funnel_lock(rsp->name, rnp->level,

						  rnp->grplo, rnp->grphi,

						  TPS("wait"));

			wait_event(rnp->exp_wq[(s >> 1) & 0x3],

			wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],

				   sync_exp_work_done(rsp,

						      &rdp->exp_workdone2, s));

			return true;
@@ -534,7 +534,7 @@ static void rcu_exp_wait_wake(struct rcu_state *rsp, unsigned long s) 
			spin_unlock(&rnp->exp_lock);

		}

		smp_mb(); /* All above changes before wakeup. */

		wake_up_all(&rnp->exp_wq[(rsp->expedited_sequence >> 1) & 0x3]);

		wake_up_all(&rnp->exp_wq[rcu_seq_ctr(rsp->expedited_sequence) & 0x3]);

	}

	trace_rcu_exp_grace_period(rsp->name, s, TPS("endwake"));

	mutex_unlock(&rsp->exp_wake_mutex);
@@ -612,9 +612,8 @@ static void _synchronize_rcu_expedited(struct rcu_state *rsp, 
	/* Wait for expedited grace period to complete. */

	rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());

	rnp = rcu_get_root(rsp);

	wait_event(rnp->exp_wq[(s >> 1) & 0x3],

		   sync_exp_work_done(rsp,

				      &rdp->exp_workdone0, s));

	wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],

		   sync_exp_work_done(rsp, &rdp->exp_workdone0, s));

	smp_mb(); /* Workqueue actions happen before return. */



	/* Let the next expedited grace period start. */