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SubjectRe: new IRQ scalability changes in 2.3.48
Andrea Arcangeli wrote:
> >Note: In many cases, spinlock_irqsave doesn't need to do the
> >spinlock_depth thing on UP. [..]
>
> It doesn't need that in SMP either.

An interrupt on another process can wake up a task and set
current->need_resched on this processor.

> >[..] However, not all cases: the code in the
> >lock region might wake up another task.
>
> If you wakeup another task you don't risk to get rescheduled before you
> drop the lock.

Waking up another task may set current->need_resched. But it can't
actually reschedule until reaching the spin_unlock_irqsave. At that
point or some low-latency time later, you need to reschedule to get low
latency.

-- Jamie

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