Hi, Thomas,
If we use (s64)cycles < 0, then how to solve the problem that a 64bit counter become negative?
Maybe we can change the "invalid" value from U64_MAX to 0? I think the performance of "cycles == 0" is better than "cycles == U64_MAX".
Huacai
On Mon, Oct 21, 2019 at 10:58 PM Thomas Gleixner tglx@linutronix.de wrote:
On Mon, 21 Oct 2019, Thomas Gleixner wrote:
On Mon, 21 Oct 2019, Huacai Chen wrote:
@@ -50,7 +50,7 @@ static int do_hres(const struct vdso_data *vd, clockid_t clk, cycles = __arch_get_hw_counter(vd->clock_mode); ns = vdso_ts->nsec; last = vd->cycle_last;
if (unlikely((s64)cycles < 0))
if (unlikely(cycles == U64_MAX)) return -1;That used to create worse code than the weird (s64) type cast which has the same effect. Did you double check that there is no change?
It still does for 32bit.