>>> On 19.12.16 at 17:38, <andrew.coop...@citrix.com> wrote:
> There is no need for the volatile cast in the timer interrupt. pit0_ticks has
> external linkage, preventing the compiler from eliding the update. This
> reduces the generated assembly from a read, local modify, write to a single
> add instruction.
I don't think external linkage is the reason here, considering the
effects of whole-program-optimization.
> --- a/xen/arch/x86/io_apic.c
> +++ b/xen/arch/x86/io_apic.c
> @@ -1485,8 +1485,7 @@ static int __init timer_irq_works(void)
> {
> unsigned long t1, flags;
>
> - t1 = pit0_ticks;
> - mb();
> + t1 = ACCESS_ONCE(pit0_ticks);
Any reason not to use the available read_atomic() here?
Jan
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