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SubjectRe: [PATCH] random: Optimize add_interrupt_randomness
Thanks, applied.

- Ted

On Wed, Feb 28, 2018 at 01:43:28PM -0800, Andi Kleen wrote:
> 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>

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