oprofile and ARM A9 hardware counter
ming.lei at canonical.com
Thu Feb 16 11:37:35 EST 2012
On Fri, Feb 17, 2012 at 12:19 AM, Peter Zijlstra <a.p.zijlstra at chello.nl> wrote:
> On Fri, 2012-02-17 at 00:12 +0800, Ming Lei wrote:
>> is triggered: u64 delta = 100 - 1000000 = 18446744073708551716.
> on x86 we do:
> int shift = 64 - x86_pmu.cntval_bits;
> s64 delta;
> delta = (new_raw_count << shift) - (prev_raw_count << shift);
> delta >>= shift;
> This deals with short overflows (on x86 the registers are typically 40
> or 48 bits wide). If the arm register is 32 you can of course also get
> there with some u32 casts.
Good idea, but it may not work if new_raw_count is bigger than prev_raw_count.
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