Commit 1c69d921 authored Dec 06, 2006 by Eric Dumazet Committed by Linus Torvalds Dec 07, 2006

[PATCH] rcu: add a prefetch() in rcu_do_batch()



On some workloads, (for example when lot of close() syscalls are done), RCU
qlen can be quite large, and RCU heads are no longer in cpu cache when
rcu_do_batch() is called.

This patch adds a prefetch() in rcu_do_batch() to give CPU a hint to bring
back cache lines containing 'struct rcu_head's.

Most list manipulations macros include prefetch(), but not open coded ones
(at least with current C compilers :) )

I got a nice speedup on a trivial benchmark (3.48 us per iteration instead
of 3.95 us on a 1.6 GHz Pentium-M)

while (1) { pipe(p); close(fd[0]); close(fd[1]);}

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

parent 9a0efbb8

kernel/rcupdate.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -235,12 +235,14 @@ static void rcu_do_batch(struct rcu_data *rdp)

		list = rdp->donelist;
		while (list) {
		next = rdp->donelist = list->next;
		next = list->next;
		prefetch(next);
		list->func(list);
		list = next;
		if (++count >= rdp->blimit)
		break;
		}
		rdp->donelist = list;

		local_irq_disable();
		rdp->qlen -= count;

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