Re: [PATCH v1 7/7] kvm/x86: Hyper-V SynIC timers

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On 11/27/2015 01:49 PM, Paolo Bonzini wrote:


On 27/11/2015 09:12, Roman Kagan wrote:
+	n = div64_u64(time_now - stimer->exp_time, stimer->count) + 1;
+	stimer->exp_time += n * stimer->count;
This is actually just a reminder calculation so I'd rather do it
directly with div64_u64_rem().

It took me a while to understand why it was a remained. :)  Expanding
Andrey's formula you get

	exp_time = exp_time + count + (time_now - exp_time) / count * count

the remainder, (time_now - exp_time) % count would be

	time_now - exp_time - (time_now - exp_time) / count * count

so -((time_now - exp_time) % count) is

	exp_time - time_now + (time_now - exp_time) / count * count

so Andrey's expression is

	exp_time = time_now + (count - (time_now - exp_time) % count)

Yeah, that looks nice.
I'll redo this way.

Paolo

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