Messages in this thread Patch in this message | | | From | Andi Kleen <> | Subject | [PATCH] random: Optimize add_interrupt_randomness | Date | Wed, 28 Feb 2018 13:43:28 -0800 |
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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
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