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rcu: Add __rcu_pending tracing to hierarchical RCU

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Add tracing to __rcu_pending() to provide information on why RCU
processing was kicked off.  This is helpful for debugging hierarchical
RCU, and might also be helpful in learning how hierarchical RCU operates.

Located-by: Anton Blanchard <[email protected]>
Tested-by: Anton Blanchard <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Cc: [email protected]
Cc: [email protected]
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Cc: [email protected]
Cc: "Paul E. McKenney" <[email protected]>
LKML-Reference: <1239683479943-git-send-email->
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Paul E. McKenney 2009-04-13 21:31:17 -07:00 • committed by Ingo Molnar
commit 7ba5c840e6
3 changed files with 90 additions and 8 deletions
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25
kernel/rcutree.c
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@ -1259,31 +1259,44 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
check_cpu_stall(rsp, rdp);
/* Is the RCU core waiting for a quiescent state from this CPU? */
if (rdp->qs_pending)
if (rdp->qs_pending) {
rdp->n_rp_qs_pending++;
return 1;
}
/* Does this CPU have callbacks ready to invoke? */
if (cpu_has_callbacks_ready_to_invoke(rdp))
if (cpu_has_callbacks_ready_to_invoke(rdp)) {
rdp->n_rp_cb_ready++;
return 1;
}
/* Has RCU gone idle with this CPU needing another grace period? */
if (cpu_needs_another_gp(rsp, rdp))
if (cpu_needs_another_gp(rsp, rdp)) {
rdp->n_rp_cpu_needs_gp++;
return 1;
}
/* Has another RCU grace period completed? */
if (ACCESS_ONCE(rsp->completed) != rdp->completed) /* outside of lock */
if (ACCESS_ONCE(rsp->completed) != rdp->completed) { /* outside lock */
rdp->n_rp_gp_completed++;
return 1;
}
/* Has a new RCU grace period started? */
if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) /* outside of lock */
if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) { /* outside lock */
rdp->n_rp_gp_started++;
return 1;
}
/* Has an RCU GP gone long enough to send resched IPIs &c? */
if (ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum) &&
((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0))
((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)) {
rdp->n_rp_need_fqs++;
return 1;
}
/* nothing to do */
rdp->n_rp_need_nothing++;
return 0;
}