From 1c69d921ed9cc6593ad4f60c0f9951cb0d62b0b4 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <dada1@cosmosbay.com>
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 <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>
---
kernel/rcupdate.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 26bb5ffe1ef1..3554b76da84c 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;
--
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