diff options
| author | Philippe Gerum <rpm@xenomai.org> | 2009-06-22 18:23:32 +0200 |
|---|---|---|
| committer | Mike Frysinger <vapier@gentoo.org> | 2009-09-16 21:28:33 -0400 |
| commit | 6b8019c85e18295466095a5778a14c1e9a067554 (patch) | |
| tree | de7b2b5ee21f5d70746821a2a5d929577cd0fed5 /arch/blackfin/kernel/entry.S | |
| parent | bc569f1a77199926be97ba6266dbea27768264df (diff) | |
Blackfin: allow high priority domains to preempt schedule_tail()
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>
Diffstat (limited to 'arch/blackfin/kernel/entry.S')
| -rw-r--r-- | arch/blackfin/kernel/entry.S | 24 |
1 files changed, 22 insertions, 2 deletions
diff --git a/arch/blackfin/kernel/entry.S b/arch/blackfin/kernel/entry.S index a9cfba9946b..3f8769b7db5 100644 --- a/arch/blackfin/kernel/entry.S +++ b/arch/blackfin/kernel/entry.S @@ -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; |