Blackfin: allow high priority domains to preempt schedule_tail() (6b8019c8) · Commits · 戴 / test

ret_from_fork is always entered with hw interrupts off, which prevents real-time domains to preempt the Linux kernel during part of the initial context switch to the new task, which could in turn raise the worst-case latency figures. To avoid this, stall the root domain stage in the interrupt pipeline to keep the scheduling tail code free from Linux-handled IRQs, then enable hardware interrupts again. Signed-off-by:

Philippe Gerum <rpm@xenomai.org> Signed-off-by:

Mike Frysinger <vapier@gentoo.org>

arch/blackfin/kernel/entry.S

+22 −2

Original line number	Diff line number	Diff line
		@@ -43,8 +43,28 @@

		ENTRY(_ret_from_fork)
		#ifdef CONFIG_IPIPE
		[--sp] = reti; /* IRQs on. */
		SP += 4;
		/*
		* Hw IRQs are off on entry, and we don't want the scheduling tail
		* code to starve high priority domains from interrupts while it
		* runs. Therefore we first stall the root stage to have the
		* virtual interrupt state reflect IMASK.
		*/
		p0.l = ___ipipe_root_status;
		p0.h = ___ipipe_root_status;
		r4 = [p0];
		bitset(r4, 0);
		[p0] = r4;
		/*
		* Then we may enable hw IRQs, allowing preemption from high
		* priority domains. schedule_tail() will do local_irq_enable()
		* since Blackfin does not define __ARCH_WANT_UNLOCKED_CTXSW, so
		* there is no need to unstall the root domain by ourselves
		* afterwards.
		*/
		p0.l = _bfin_irq_flags;
		p0.h = _bfin_irq_flags;
		r4 = [p0];
		sti r4;
		#endif /* CONFIG_IPIPE */
		SP += -12;
		call _schedule_tail;

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