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List:       linux-kernel
Subject:    Re: [RFC] Merge softirq, local_irq_count, local_bh_count
From:       Russell King <rmk () arm ! linux ! org ! uk>
Date:       2000-07-27 22:22:38
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Keith Owens writes:
> Except for the places where cpu is a variable instead of smp_processor_id(),
> those places might generate array access code.

They shouldn't do - GCC should realise that code like:

	int this_cpu = 0;

	array_access[this_cpu].foo = 0;
	array_access[this_cpu].bar = 1;

can be optimised.  So long as "this_cpu" remains an auto variable, then
it should be ok.

> I thought about using a
> single set of macros and always defining irq_stat[NR_CPUS], trusting to
> gcc to optimize the array access away for UP but decided to err on the
> side of caution.

We relied on it before, so why can't we rely on it again?

> As for readability, almost all the existing code
> defines SMP and UP versions, at least this patch reduces to one
> definition instead of one per arch with subtly different definitions.

There's no argument there.  Its only that it can be improved further
with very little effort.
   _____
  |_____| ------------------------------------------------- ---+---+-
  |   |         Russell King        rmk@arm.linux.org.uk      --- ---
  | | | |   http://www.arm.linux.org.uk/~rmk/aboutme.html    /  /  |
  | +-+-+                                                     --- -+-
  /   |               THE developer of ARM Linux              |+| /|\
 /  | | |                                                     ---  |
    +-+-+ -------------------------------------------------  /\\\  |

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