lkml.org 
[lkml]   [2018]   [Feb]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] random: Optimize add_interrupt_randomness
Date
From: Andi Kleen <ak@linux.intel.com>

add_interrupt_randomess always wakes up
code blocking on /dev/random. This wake up is done
unconditionally. Unfortunately this means all interrupts
take the wait queue spinlock, which can be rather expensive
on large systems processing lots of interrupts.

We saw 1% cpu time spinning on this on a large macro workload
running on a large system.

I believe it's a recent regression (?)

Always check if there is a waiter on the wait queue
before waking up. This check can be done without
taking a spinlock.

1.06% 10460 [kernel.vmlinux] [k] native_queued_spin_lock_slowpath
|
---native_queued_spin_lock_slowpath
|
--0.57%--_raw_spin_lock_irqsave
|
--0.56%--__wake_up_common_lock
credit_entropy_bits
add_interrupt_randomness
handle_irq_event_percpu
handle_irq_event
handle_edge_irq
handle_irq
do_IRQ
common_interrupt

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
drivers/char/random.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index e5b3d3ba4660..64a897a2888f 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -709,7 +709,8 @@ static void credit_entropy_bits(struct entropy_store *r, int nbits)
}

/* should we wake readers? */
- if (entropy_bits >= random_read_wakeup_bits) {
+ if (entropy_bits >= random_read_wakeup_bits &&
+ wq_has_sleeper(&random_read_wait)) {
wake_up_interruptible(&random_read_wait);
kill_fasync(&fasync, SIGIO, POLL_IN);
}
--
2.14.3
\
 
 \ /
  Last update: 2018-02-28 22:44    [W:0.961 / U:2.600 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site