On Tue, Jun 9, 2020 at 3:04 AM Honnappa Nagarahalli
<honnappa.nagaraha...@arm.com> wrote:
>
> get_tsc_freq uses 'nanosleep' system call to calculate the CPU
> frequency. However, 'nanosleep' results in the process getting
> un-scheduled. The kernel saves and restores the PMU state. This
> ensures that the PMU cycles are not counted towards a sleeping
> process. When RTE_ARM_EAL_RDTSC_USE_PMU is defined, this results
> in incorrect CPU frequency calculation. This logic is replaced
> with generic counter based loop.
>
> Bugzilla ID: 450
> Fixes: af75078fece3 ("first public release")
The Fix looks good to me.
The Fixes is not correct. It should be the patch where
RTE_ARM_EAL_RDTSC_USE_PMU got introduced.
> Cc: sta...@dpdk.org
>
> Signed-off-by: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.w...@arm.com>
> Reviewed-by: Dharmik Thakkar <dharmik.thak...@arm.com>
> Reviewed-by: Phil Yang <phil.y...@arm.com>
>
> ---
> lib/librte_eal/arm/include/rte_cycles_64.h | 45 +++++++++++++++++++---
> lib/librte_eal/arm/rte_cycles.c | 24 ++++++++++--
> 2 files changed, 61 insertions(+), 8 deletions(-)
>
> diff --git a/lib/librte_eal/arm/include/rte_cycles_64.h
> b/lib/librte_eal/arm/include/rte_cycles_64.h
> index da557b6a1..6fc352036 100644
> --- a/lib/librte_eal/arm/include/rte_cycles_64.h
> +++ b/lib/librte_eal/arm/include/rte_cycles_64.h
> @@ -11,6 +11,36 @@ extern "C" {
>
> #include "generic/rte_cycles.h"
>
> +/** Read generic counter frequency */
> +static inline uint64_t
I prefer to have __rte_allways_inline
> +__rte_rd_generic_cntr_freq(void)
I think, the generic counter is confusing, I think, since the symbol
is exposed due to placed in
header file, it is better to change, __rte_arm64_cntfrq()
> +{
> + uint64_t freq;
> +
> + asm volatile("mrs %0, cntfrq_el0" : "=r" (freq));
> + return freq;
> +}
> +
> +/** Read generic counter */
> +static inline uint64_t
Likewise, __rte_arm64_cntvct()
> +__rte_rd_generic_cntr(void)
> +{
> + uint64_t tsc;
> +
> + asm volatile("mrs %0, cntvct_el0" : "=r" (tsc));
> + return tsc;
> +}
> +
> +static inline uint64_t
> +__rte_rd_generic_cntr_precise(void)
__rte_arm64_cntfrq_precise()
> +{
> + uint64_t tsc;
> +
> + asm volatile("isb" : : : "memory");
> + asm volatile("mrs %0, cntvct_el0" : "=r" (tsc));
> + return tsc;
> +}
> +
> /**
> * Read the time base register.
> *
> @@ -25,10 +55,7 @@ extern "C" {
> static inline uint64_t
> rte_rdtsc(void)
> {
> - uint64_t tsc;
> -
> - asm volatile("mrs %0, cntvct_el0" : "=r" (tsc));
> - return tsc;
> + return __rte_rd_generic_cntr();
> }
> #else
> /**
> @@ -49,14 +76,22 @@ rte_rdtsc(void)
> * asm volatile("msr pmcr_el0, %0" : : "r" (val));
> *
> */
> +
> +/** Read PMU cycle counter */
> static inline uint64_t
> -rte_rdtsc(void)
> +__rte_rd_pmu_cycle_cntr(void)
> {
> uint64_t tsc;
>
> asm volatile("mrs %0, pmccntr_el0" : "=r"(tsc));
> return tsc;
> }
> +
> +static inline uint64_t
> +rte_rdtsc(void)
> +{
> + return __rte_rd_pmu_cycle_cntr();
> +}
> #endif
>
> static inline uint64_t
> diff --git a/lib/librte_eal/arm/rte_cycles.c b/lib/librte_eal/arm/rte_cycles.c
> index 3500d523e..92c87a8a4 100644
> --- a/lib/librte_eal/arm/rte_cycles.c
> +++ b/lib/librte_eal/arm/rte_cycles.c
> @@ -3,14 +3,32 @@
> */
>
> #include "eal_private.h"
> +#include "rte_cycles.h"
>
> uint64_t
> get_tsc_freq_arch(void)
> {
> #if defined RTE_ARCH_ARM64 && !defined RTE_ARM_EAL_RDTSC_USE_PMU
> - uint64_t freq;
> - asm volatile("mrs %0, cntfrq_el0" : "=r" (freq));
> - return freq;
> + return __rte_rd_generic_cntr_freq();
> +#elif defined RTE_ARCH_ARM64 && defined RTE_ARM_EAL_RDTSC_USE_PMU
> + /* Use the generic counter ticks to calculate the PMU
> + * cycle frequency.
> + */
> + uint64_t gcnt_ticks;
> + uint64_t start_ticks, cur_ticks;
> + uint64_t start_pmu_cycles, end_pmu_cycles;
> +
> + /* Number of ticks for 1/10 second */
> + gcnt_ticks = __rte_rd_generic_cntr_freq() / 10;
> +
> + start_ticks = __rte_rd_generic_cntr_precise();
> + start_pmu_cycles = rte_rdtsc_precise();
> + do {
> + cur_ticks = __rte_rd_generic_cntr();
> + } while ((cur_ticks - start_ticks) < gcnt_ticks);
> + end_pmu_cycles = rte_rdtsc_precise();
> +
> + return ((end_pmu_cycles - start_pmu_cycles) * 10);
Good thought. On the plus side, it will reduce the boot time by .9 sec.
> #else
> return 0;
With above changes:
Acked-by: Jerin Jacob <jer...@marvell.com>
> #endif
> --
> 2.17.1
>
