Getting extremely volatile results from get_tsc_hz(). Here's what I get from
10 successive calls:
freq=2660000000
freq=3220000000
freq=3740000000
freq=3870000000
freq=3830000000
freq=4060000000
freq=3370000000
freq=3820000000
freq=7370000000
freq=4970000000
Please see the last comment for the reason (and other comments inline).
On 2020-05-06 15:01 GMT+0300 Fady Bader wrote:
> Implemented the needed Windows eal timer functions.
>
> Signed-off-by: Fady Bader <f...@mellanox.com>
> ---
[snip]
> diff --git a/lib/librte_eal/windows/eal_timer.c
> b/lib/librte_eal/windows/eal_timer.c
> new file mode 100644
> index 000000000..108f66b54
> --- /dev/null
> +++ b/lib/librte_eal/windows/eal_timer.c
> @@ -0,0 +1,96 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright 2020 Mellanox Technologies, Ltd
> + */
> +#include <inttypes.h>
> +#include <time.h>
> +
> +#include <rte_windows.h>
> +#include <rte_common.h>
> +#include <rte_log.h>
> +#include <rte_cycles.h>
> +#include <rte_eal.h>
> +#include <rte_errno.h>
#include "eal_private.h", without it:
../../../lib/librte_eal/windows/eal_timer.c: In function ‘rte_eal_timer_init’:
../../../lib/librte_eal/windows/eal_timer.c:108:2: warning: implicit
declaration of function ‘set_tsc_freq’; did you mean ‘get_tsc_freq’?
[-Wimplicit-function-declaration]
108 | set_tsc_freq();
> +
> +#define US_PER_SEC 1E6
> +#define CYC_PER_10MHZ 1E7
> +
> +/* The frequency of the RDTSC timer resolution */
> +static uint64_t eal_tsc_resolution_hz;
> +
At top level:
../../../lib/librte_eal/windows/eal_timer.c:20:17: warning:
‘eal_tsc_resolution_hz’ defined but not used [-Wunused-variable]
20 | static uint64_t eal_tsc_resolution_hz;
Note: set_tsc_freq() already caches frequency you calculate here.
> + due_time.QuadPart = -(us * 10);
> + if (!SetWaitableTimer(timer, &due_time, 0, NULL, NULL, FALSE)) {
> + CloseHandle(timer);
> + RTE_LOG_WIN32_ERR("SetWaitableTimer()");
RTE_LOG_WIN32_ERR() uses GetLastError(), the value of which may be overridden
by a successful call to CloseHandle().
> + rte_errno = EINVAL;
> + return;
> + }
> + /* start wait for timer for us microseconds */
> + WaitForSingleObject(timer, INFINITE);
> + CloseHandle(timer);
> +}
> +
> +uint64_t
> +get_tsc_freq(void)
> +{
> + LARGE_INTEGER t_start, t_end, elapsed_us;
> + LARGE_INTEGER frequency;
> + uint64_t tsc_hz;
> +
> + if (QueryPerformanceFrequency(&frequency) == 0) {
> + RTE_LOG_WIN32_ERR("QueryPerformanceFrequency()");
> + return 0;
> + }
> +
> + if (QueryPerformanceCounter(&t_start) != 0) {
Per MSDN, QueryPerformanceFrequency() and QueryPerformanceCounter() always
succeed on all supported Windows versions.
> + uint64_t end, start = rte_get_tsc_cycles();
> +
> + rte_delay_us(US_PER_SEC / 10); /* 1/10 second */
Did you mean rte_delay_us_sleep()? rte_delay_us() assumes TSC frequency is
already available. With this fix, results become stable.
--
Dmitry Kozlyuk
