Haavard Skinnemoen wrote:
Hi everyone,
I've put up an updated set of patches for AVR32 support at
http://avr32linux.org/twiki/bin/view/Main/LinuxPatches
The most interesting patch probably is
http://avr32linux.org/twiki/pub/Main/LinuxPatches/avr32-arch-2.patch
which, at 544K, is too large to attach here. Please let me know if you
want me to do it anyway.
Anyone want to have a look at this? I understand that a full review is
a huge job, but I'd appreciate a pointer or two in the general
direction that I need to take this in order to get it acceptable for
mainline.
Hi,
+void cpu_idle(void)
+{
+ /* endless idle loop with no priority at all */
+ while (1) {
+ /* TODO: Enter sleep mode */
+ if (need_resched())
+ schedule();
+ }
+}
AFAIKS, this is buggy.
need_resched() translates to a test_bit, which doesn't have any barriers,
so it could be optimised away completely. And if you're intending to use
preempt, you need to have preemption disabled in the idle loop.
Documentation/sched-arch.txt attempts to explain, and something like
arm26's cpu_idle() is a nice, simple example to follow.
Actually, I'm wrong about the test_bit. It casts to volatile there, which
is probably why you don't end up with infinite loops. Still, it would be
nicer to have an explicit barrier (eg. cpu_relax()).
Why do we cast to volatile in places like this? Linus? I don't see why
test_bit() should be any more "special" than the & operator. What's more,
some architectures do cast and others don't, which is just insane.
--
SUSE Labs, Novell Inc.
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