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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: 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>
This commit is contained in:
Eric Dumazet 2006-12-06 20:38:44 -08:00 committed by Linus Torvalds
parent 9a0efbb879
commit 1c69d921ed
1 changed files with 3 additions and 1 deletions
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4
kernel/rcupdate.c
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@ -235,12 +235,14 @@ static void rcu_do_batch(struct rcu_data *rdp)
list = rdp->donelist; list = rdp->donelist;
while (list) { while (list) {
next = rdp->donelist = list->next; next = list->next;
prefetch(next);
list->func(list); list->func(list);
list = next; list = next;
if (++count >= rdp->blimit) if (++count >= rdp->blimit)
break; break;
} }
rdp->donelist = list;
local_irq_disable(); local_irq_disable();
rdp->qlen -= count; rdp->qlen -= count;