Scott Cheloha:
> --- lib/libc/arch/amd64/gen/usertc.c 8 Jul 2020 09:17:48 -0000 1.2
> +++ lib/libc/arch/amd64/gen/usertc.c 25 Jul 2020 17:50:38 -0000
> @@ -21,9 +21,12 @@
> static inline u_int
> rdtsc(void)
> {
> - uint32_t hi, lo;
> - asm volatile("rdtsc" : "=a"(lo), "=d"(hi));
> - return ((uint64_t)lo)|(((uint64_t)hi)<<32);
> + uint32_t lo;
> +
> + asm volatile("lfence");
> + asm volatile("rdtsc" : "=a"(lo) : : "rdx");
Is there a guarantee that two separate asm()s will not be reordered?
> +
> + return lo;
> }
>
> static int
> --- sys/arch/amd64/amd64/tsc.c 6 Jul 2020 13:33:06 -0000 1.19
> +++ sys/arch/amd64/amd64/tsc.c 25 Jul 2020 17:50:38 -0000
> @@ -211,7 +211,12 @@ cpu_recalibrate_tsc(struct timecounter *
> u_int
> tsc_get_timecount(struct timecounter *tc)
> {
> - return rdtsc() + curcpu()->ci_tsc_skew;
> + uint32_t lo;
> +
> + asm volatile("lfence");
> + asm volatile("rdtsc" : "=a"(lo) : : "rdx");
> +
> + return lo + curcpu()->ci_tsc_skew;
> }
>
> void
>
I'd just do s/rdtsc/rdtsc_lfence/, which would agree well with the
rest of the file.
--
Christian "naddy" Weisgerber [email protected]
