On 08/07/15 22:33, Henrik Gramner wrote: > Improves the accuracy of measurements, especially in short sections. > > To quote the Intel 64 and IA-32 Architectures Software Developer's Manual: > "The RDTSC instruction is not a serializing instruction. It does not > necessarily > wait until all previous instructions have been executed before reading the > counter. > Similarly, subsequent instructions may begin execution before the read > operation > is performed. If software requires RDTSC to be executed only after all > previous > instructions have completed locally, it can either use RDTSCP (if the > processor > supports that instruction) or execute the sequence LFENCE;RDTSC." > > SSE2 is a requirement for lfence so only use it on SSE2-capable systems. > Prefer lfence;rdtsc over rdtscp since rdtscp is supported on fewer systems. > --- > libavutil/x86/timer.h | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) >
Shouldn't hurt. lu _______________________________________________ libav-devel mailing list [email protected] https://lists.libav.org/mailman/listinfo/libav-devel
