On 2020-04-27 15:20 GMT+0300 Fady Bader wrote:
> Implemented the needed Windows eal timer functions.
[snip]
> +void
> +rte_delay_us_sleep(unsigned int us)
> +{
> + HANDLE timer;
> + LARGE_INTEGER li_due_time;
Here usually comes a blank line.
> + /* create waitable timer */
> + timer = CreateWaitableTimer(NULL, TRUE, NULL);
> + if (!timer) {
> + RTE_LOG_WIN32_ERR("CreateWaitableTimer()");
> + rte_errno = ENOMEM;
> + return;
> + }
> +
> + /* set us microseconds time for timer */
> + li_due_time.QuadPart = -(us * 10);
The comment is still misleading.
[snip]
> +uint64_t
> +get_tsc_freq(void)
> +{
> + uint64_t tsc_freq;
> + LARGE_INTEGER Frequency;
> +
> + QueryPerformanceFrequency(&Frequency);
> +
> + /*
> + * Mulitply by 1K to obtain the true frequency of the CPU
> + * it was noted in the MSDN "in many cases, QueryPerformanceFrequency
> + * returns the TSC frequency divided by 1024"
> + */
> + tsc_freq = ((uint64_t)Frequency.QuadPart * 1024);
> +
> + return tsc_freq;
> +}
Extended quote from MSDN:
Cases might exist where QueryPerformanceFrequency doesn't return the
actual frequency of the hardware tick generator. For example, in many
cases, QueryPerformanceFrequency returns the TSC frequency divided by
1024; and on Hyper-V, the performance counter frequency is always 10
MHz when the guest virtual machine runs under a hypervisor that
implements the hypervisor version 1.0 interface. As a result, don't
assume that QueryPerformanceFrequency will return the precise TSC
frequency.
https://docs.microsoft.com/en-us/windows/win32/sysinfo/acquiring-high-resolution-time-stamps
"In many cases" is pretty vague, we can't distinguish such cases.
Here's what I observe on my QEMU guest ("ticks" is Win32 API, "tsc" is RDTSC):
freq = 100000000 Hz # note: 100 MHz, not 10 MHz
delta (ticks) = 100401071 # Sleep(1000)
delta (secs) = 1.004011 # delta (ticks) / freq
delta (tsc) = 3460948332 # roughly CPU clock frequency
tsc / tick = 34.471229
I suggest measuring a real-time delay with rte_get_tsc_cycles() from arch/
as other EALs do when HPET is not available or configured. This is
discouraged by MSDN, but its reasons seem irrelevant for DPDK.
--
Dmitry Kozlyuk
