Re: [PATCH] locking: Revert switching guards to _irq_{disable,enable}()

[Thomas Gleixner <tglx@kernel.org>]

On Thu, Aug 27 2026 at 10:30, Thomas Gleixner wrote:
> On Tue, Aug 25 2026 at 16:28, Boqun Feng wrote:
> So you can get away with:
>
> raw_local_irq_save(flags)
> {
> 	flags = count;
> 	if (!count)
>         	arch_local_irq_disable();
>         count++;
> }
>
> raw_local_irq_restore(flags)
> {
> 	if (!(count = flags))
>         	arch_local_irq_enable();
> }
>
> raw_local_irq_disable()
> {
>         arch_local_irq_disable();
>         count = 1;
> }
>
> raw_local_irq_enable()
> {
>         count = 0;
>         arch_local_irq_enable();
> }

Actually it can be done way simpler because the nasty case of

         scoped_guard(lock_irqsave, lock) {
         	unlock_irq(lock);
                lock_irq(lock);
         }

is only valid for a single lock guard, because if it's nested then the
outer lock would lose the interrupt disabled protection. Anything else
would be a bug on its own and would have long ago blown up in our face.

So we can completely ignore flags.

raw_local_irq_save(flags)
{
 	if (!count)
         	arch_local_irq_disable();
        count++;
}

raw_local_irq_restore(flags)
{
 	if (!--count)
         	arch_local_irq_enable();
}

raw_local_irq_disable()
{
         arch_local_irq_disable();
         count++;
}

raw_local_irq_enable()
{
         count--;
         arch_local_irq_enable();
}

with a copious amount of debug machinery to catch any oddballs.

Also note that this never uses irqsave/restore because historically that
has been way slower than CLI/STI.

A decade+ ago this used to be up to 30%, but micro architectures
optimized for it. Still on a SKL it's ~14% and on a Zen3 ~8% slower.

Thanks,

        tglx