From 1c69d921ed9cc6593ad4f60c0f9951cb0d62b0b4 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 6 Dec 2006 20:38:44 -0800 Subject: [PATCH] [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 Cc: "Paul E. McKenney" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/rcupdate.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 26bb5ffe1ef..3554b76da84 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -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; -- 2.20.1