On Fri, 9 Nov 2007, Andi Kleen wrote:
>
> > There is an interrupt enable overhead of 48 cycles that would be good to
> > be able to eliminate (Kernel code usually moves counter increments into
> > a neighboring interrupt disable section so that __ function can be used).
>
> Replace the push flags ; popf with test $IFMASK,flags ; jz 1f; sti ; 1:
> That will likely make it much faster (but also bigger)
Well maybe we should change local_irq_save/restore in general?
The result would be:
if (!in_interrupt())
local_irq_disable()
<critical section>
if (!in_interrupt())
local_irq_enable();
Somehow we need to remember that we disabled interrupts.
Then it get more complicated.
int interrupts_disabled = 0;
if (!in_interrupt()) {
local_irq_disable():
interrrupts_disabled = 1;
}
<critical section>
if (interrupts_disabled)
local_irq_enable();
Not sure that this actually better.
> The only problem is that there might be some code who relies on
> restore_flags() restoring other flags that IF, but at least for interrupts
> and local_irq_save/restore it should be fine to change.
The statistics code surely does not rely on that.
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