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rcu: Add event-tracing for RCU callback invocation

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There was recently some controversy about the overhead of invoking RCU
callbacks.  Add TRACE_EVENT()s to obtain fine-grained timings for the
start and stop of a batch of callbacks and also for each callback invoked.

Signed-off-by: Paul E. McKenney <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
This commit is contained in:
Paul E. McKenney 2011-06-17 15:53:19 -07:00 • committed by Paul E. McKenney
commit 29c00b4a1d
6 changed files with 219 additions and 54 deletions
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15
kernel/rcutree.c
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@ -52,6 +52,9 @@
#include <linux/prefetch.h>
#include "rcutree.h"
#include <trace/events/rcu.h>
#include "rcu.h"
/* Data structures. */
@ -1190,17 +1193,22 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
{
unsigned long flags;
struct rcu_head *next, *list, **tail;
int count;
int bl, count;
/* If no callbacks are ready, just return.*/
if (!cpu_has_callbacks_ready_to_invoke(rdp))
if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
trace_rcu_batch_start(0, 0);
trace_rcu_batch_end(0);
return;
}
/*
* Extract the list of ready callbacks, disabling to prevent
* races with call_rcu() from interrupt handlers.
*/
local_irq_save(flags);
bl = rdp->blimit;
trace_rcu_batch_start(rdp->qlen, bl);
list = rdp->nxtlist;
rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
*rdp->nxttail[RCU_DONE_TAIL] = NULL;
@ -1218,11 +1226,12 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
debug_rcu_head_unqueue(list);
__rcu_reclaim(list);
list = next;
if (++count >= rdp->blimit)
if (++count >= bl)
break;
}
local_irq_save(flags);
trace_rcu_batch_end(count);
/* Update count, and requeue any remaining callbacks. */
rdp->qlen -= count;