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Re: Critical section
On Thu, Nov 27, 2014 at 1:38 AM, Matt Thomas <matt%3am-software.com@localhost> wrote:
> That is not true. If the softint thread sleeps, control is returned back
> to the preempted lwp.
You're right. I keep forgetting how softint works. Sigh.
- Generic soft interrupt is implemented as kthread, and is not
preemptive. No chance to be executed during critical sections.
- "Fast" soft interrupt is called from MD interrupt dispatch code,
that switches stack onto on per-CPU, per-interrupt-level pre-allocated
thread (LWP) to execute soft interrupts.
- When these soft interrupts block and enter scheduler, the control
is directly back to the "interrupted" LWP.
- Which means that "fast" soft interrupt precedes preemptiveness; MD
soft interrupt dispatcher ignores l_nopreempt.
(Calling "interrupted" threads as "preempted" threads is confusing.
It's a pity that these are called differently (l_switchto, pinned,
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