linux-kernel - Re: [PATCH] semaphore: use raw_spin_lock_irq instead of raw_spin_lock

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Date:   Thu, 21 Jun 2018 15:50:14 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Matthew Wilcox <matthew@....cx>, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] semaphore: use raw_spin_lock_irq instead of
 raw_spin_lock_irqsave


* Mikulas Patocka <mpatocka@...hat.com> wrote:

> The sleeping functions down, down_interruptible, down_killable and
> down_timeout can't be called with interrupts disabled, so we don't have to
> save and restore interrupt flag.
> 
> This patch avoids the costly pushf and popf instructions on the semaphore
> path.
> 
> Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
> 
> ---
>  kernel/locking/semaphore.c |   21 ++++++++-------------
>  1 file changed, 8 insertions(+), 13 deletions(-)

I've applied this to the locking tree, I suspect we can do this on the condition 
that it doesn't explode in early boot code (which has irqs disabled) and doesn't 
generate early boot lockdep splats either.

Thanks,

	Ingo