Hi Jerin,
Thanks for the comments.
> -----Original Message-----
> From: Jerin Jacob <jerinjac...@gmail.com>
> Sent: Wednesday, June 24, 2020 7:51 AM
> To: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>
> Cc: dpdk-dev <dev@dpdk.org>; jer...@marvell.com;
> hemant.agra...@nxp.com; akhil.go...@nxp.com; ogerl...@mellanox.com;
> Ajit Khaparde (ajit.khapa...@broadcom.com)
> <ajit.khapa...@broadcom.com>; ruigeng.w...@arm.com; Dharmik Thakkar
> <dharmik.thak...@arm.com>; Phil Yang <phil.y...@arm.com>; dpdk stable
> <sta...@dpdk.org>
> Subject: Re: [dpdk-dev] [PATCH] eal: generic counter based loop for CPU freq
> calculation
>
> 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.
Ok, will dig that out.
>
>
> > 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()
Ok, makes sense.
>
> > +{
> > + 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)
I will change this to __rte_arm64_pmccntr
> > {
> > 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
> >
