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Commit 1c69d921 authored by Eric Dumazet's avatar Eric Dumazet Committed by Linus Torvalds
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[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: default avatarEric Dumazet <dada1@cosmosbay.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus 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;