Messages in this thread | | | From | Valentin Schneider <> | Subject | preempt_schedule_irq() loop question | Date | Wed, 16 Jan 2019 12:50:42 +0000 |
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Hi,
I've been wandering around preempt_schedule_irq() in sched/core.c, and got curious regarding how the arch code calls it.
The main part of preempt_schedule_irq() is:
do { preempt_disable(); local_irq_enable(); __schedule(true); local_irq_disable(); sched_preempt_enable_no_resched(); } while (need_resched());
Yet all the arch entry.S I looked at (I stopped after arm64, arm, x86_32, MIPS, powerpc) wrap the call to preempt_schedule_irq() in another
do { ... } while (need_resched())
For instance, this is what's done in arm64:
1: bl preempt_schedule_irq // irq en/disable is done inside ldr x0, [tsk, #TSK_TI_FLAGS] // get new tasks TI_FLAGS tbnz x0, #TIF_NEED_RESCHED, 1b // needs rescheduling?
I naively thought this could be attributed to something like preempt_schedule_irq() historically not having an inner loop, but it seems to have been there since the beginning of time (or at least up to the point where the git history stops).
I don't see why we need to have these nested loops - AFAICT the one in preempt_schedule_irq() would suffice. What am I missing?
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