Re: [PATCH 2/4] target/arm: Abstract the generic timer frequency
On Tue, 3 Dec 2019, at 04:42, Peter Maydell wrote:
> On Thu, 28 Nov 2019 at 05:44, Andrew Jeffery wrote:
> >
> > Prepare for SoCs such as the ASPEED AST2600 whose firmware configures
> > CNTFRQ to values significantly larger than the static 62.5MHz value
> > currently derived from GTIMER_SCALE. As the OS potentially derives its
> > timer periods from the CNTFRQ value the lack of support for running
> > QEMUTimers at the appropriate rate leads to sticky behaviour in the
> > guest.
> >
> > Substitute the GTIMER_SCALE constant with use of a helper to derive the
> > period from gt_cntfrq stored in struct ARMCPU. Initially set gt_cntfrq
> > to the frequency associated with GTIMER_SCALE so current behaviour is
> > maintained.
> >
> > Signed-off-by: Andrew Jeffery
>
> > +static inline unsigned int gt_cntfrq_period_ns(ARMCPU *cpu)
> > +{
> > +/* XXX: Could include qemu/timer.h to get NANOSECONDS_PER_SECOND? */
> > +const unsigned int ns_per_s = 1000 * 1000 * 1000;
> > +return ns_per_s > cpu->gt_cntfrq ? ns_per_s / cpu->gt_cntfrq : 1;
> > +}
>
> This function is named gt_cntfrq_period_ns()...
>
> > static uint64_t gt_virt_cnt_read(CPUARMState *env, const ARMCPRegInfo *ri)
> > {
> > +ARMCPU *cpu = env_archcpu(env);
> > +
> > /* Currently we have no support for QEMUTimer in linux-user so we
> > * can't call gt_get_countervalue(env), instead we directly
> > * call the lower level functions.
> > */
> > -return cpu_get_clock() / GTIMER_SCALE;
> > +return cpu_get_clock() / gt_cntfrq_period(cpu);
> > }
>
> ...but here we call gt_cntfrq_period(), which doesn't exist,
> and indeed at least one of the patchew build systems reported
> it as a compile failure.
>
Ah yep, I failed to test user mode after renaming the function and missed this.
I haven't seen an alert from patchew though, I wonder where that got to?
Andrew
Re: [PATCH 2/4] target/arm: Abstract the generic timer frequency
On Thu, 28 Nov 2019 at 05:44, Andrew Jeffery wrote:
>
> Prepare for SoCs such as the ASPEED AST2600 whose firmware configures
> CNTFRQ to values significantly larger than the static 62.5MHz value
> currently derived from GTIMER_SCALE. As the OS potentially derives its
> timer periods from the CNTFRQ value the lack of support for running
> QEMUTimers at the appropriate rate leads to sticky behaviour in the
> guest.
>
> Substitute the GTIMER_SCALE constant with use of a helper to derive the
> period from gt_cntfrq stored in struct ARMCPU. Initially set gt_cntfrq
> to the frequency associated with GTIMER_SCALE so current behaviour is
> maintained.
>
> Signed-off-by: Andrew Jeffery
> +static inline unsigned int gt_cntfrq_period_ns(ARMCPU *cpu)
> +{
> +/* XXX: Could include qemu/timer.h to get NANOSECONDS_PER_SECOND? */
> +const unsigned int ns_per_s = 1000 * 1000 * 1000;
> +return ns_per_s > cpu->gt_cntfrq ? ns_per_s / cpu->gt_cntfrq : 1;
> +}
This function is named gt_cntfrq_period_ns()...
> static uint64_t gt_virt_cnt_read(CPUARMState *env, const ARMCPRegInfo *ri)
> {
> +ARMCPU *cpu = env_archcpu(env);
> +
> /* Currently we have no support for QEMUTimer in linux-user so we
> * can't call gt_get_countervalue(env), instead we directly
> * call the lower level functions.
> */
> -return cpu_get_clock() / GTIMER_SCALE;
> +return cpu_get_clock() / gt_cntfrq_period(cpu);
> }
...but here we call gt_cntfrq_period(), which doesn't exist,
and indeed at least one of the patchew build systems reported
it as a compile failure.
thanks
-- PMM
Re: [PATCH 2/4] target/arm: Abstract the generic timer frequency
On Thu, 28 Nov 2019, at 19:16, Cédric Le Goater wrote:
> On 28/11/2019 06:45, Andrew Jeffery wrote:
> > Prepare for SoCs such as the ASPEED AST2600 whose firmware configures
> > CNTFRQ to values significantly larger than the static 62.5MHz value
> > currently derived from GTIMER_SCALE. As the OS potentially derives its
> > timer periods from the CNTFRQ value the lack of support for running
> > QEMUTimers at the appropriate rate leads to sticky behaviour in the
> > guest.
> >
> > Substitute the GTIMER_SCALE constant with use of a helper to derive the
> > period from gt_cntfrq stored in struct ARMCPU. Initially set gt_cntfrq
> > to the frequency associated with GTIMER_SCALE so current behaviour is
> > maintained.
> >
> > Signed-off-by: Andrew Jeffery
> > ---
> > target/arm/cpu.c| 2 ++
> > target/arm/cpu.h| 10 ++
> > target/arm/helper.c | 10 +++---
> > 3 files changed, 19 insertions(+), 3 deletions(-)
> >
> > diff --git a/target/arm/cpu.c b/target/arm/cpu.c
> > index 7a4ac9339bf9..5698a74061bb 100644
> > --- a/target/arm/cpu.c
> > +++ b/target/arm/cpu.c
> > @@ -974,6 +974,8 @@ static void arm_cpu_initfn(Object *obj)
> > if (tcg_enabled()) {
> > cpu->psci_version = 2; /* TCG implements PSCI 0.2 */
> > }
> > +
> > +cpu->gt_cntfrq = NANOSECONDS_PER_SECOND / GTIMER_SCALE;
> > }
> >
> > static Property arm_cpu_reset_cbar_property =
> > diff --git a/target/arm/cpu.h b/target/arm/cpu.h
> > index 83a809d4bac4..666c03871fdf 100644
> > --- a/target/arm/cpu.h
> > +++ b/target/arm/cpu.h
> > @@ -932,8 +932,18 @@ struct ARMCPU {
> > */
> > DECLARE_BITMAP(sve_vq_map, ARM_MAX_VQ);
> > DECLARE_BITMAP(sve_vq_init, ARM_MAX_VQ);
> > +
> > +/* Generic timer counter frequency, in Hz */
> > +uint64_t gt_cntfrq;
> > };
> >
> > +static inline unsigned int gt_cntfrq_period_ns(ARMCPU *cpu)
> > +{
> > +/* XXX: Could include qemu/timer.h to get NANOSECONDS_PER_SECOND? */
> > +const unsigned int ns_per_s = 1000 * 1000 * 1000;
> > +return ns_per_s > cpu->gt_cntfrq ? ns_per_s / cpu->gt_cntfrq : 1;
> > +}
>
> Are you inlining this helper for performance reasons ?
Originally I was going to do it as a macro in order to avoid redundantly
scattering
the calculation around. My thought was to use a macro as it's a simple
calculation,
but then figured it was a bit nicer as a function for type safety. I already
had it as a
macro in the header, so it was the least effort to switch it to a static inline
and leave
it where it was :) So that's the justification, mostly just evolution of
thought process.
Performance was also a consideration but I've done no measurements.
Andrew
Re: [PATCH 2/4] target/arm: Abstract the generic timer frequency
On 28/11/2019 06:45, Andrew Jeffery wrote:
> Prepare for SoCs such as the ASPEED AST2600 whose firmware configures
> CNTFRQ to values significantly larger than the static 62.5MHz value
> currently derived from GTIMER_SCALE. As the OS potentially derives its
> timer periods from the CNTFRQ value the lack of support for running
> QEMUTimers at the appropriate rate leads to sticky behaviour in the
> guest.
>
> Substitute the GTIMER_SCALE constant with use of a helper to derive the
> period from gt_cntfrq stored in struct ARMCPU. Initially set gt_cntfrq
> to the frequency associated with GTIMER_SCALE so current behaviour is
> maintained.
>
> Signed-off-by: Andrew Jeffery
> ---
> target/arm/cpu.c| 2 ++
> target/arm/cpu.h| 10 ++
> target/arm/helper.c | 10 +++---
> 3 files changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
> index 7a4ac9339bf9..5698a74061bb 100644
> --- a/target/arm/cpu.c
> +++ b/target/arm/cpu.c
> @@ -974,6 +974,8 @@ static void arm_cpu_initfn(Object *obj)
> if (tcg_enabled()) {
> cpu->psci_version = 2; /* TCG implements PSCI 0.2 */
> }
> +
> +cpu->gt_cntfrq = NANOSECONDS_PER_SECOND / GTIMER_SCALE;
> }
>
> static Property arm_cpu_reset_cbar_property =
> diff --git a/target/arm/cpu.h b/target/arm/cpu.h
> index 83a809d4bac4..666c03871fdf 100644
> --- a/target/arm/cpu.h
> +++ b/target/arm/cpu.h
> @@ -932,8 +932,18 @@ struct ARMCPU {
> */
> DECLARE_BITMAP(sve_vq_map, ARM_MAX_VQ);
> DECLARE_BITMAP(sve_vq_init, ARM_MAX_VQ);
> +
> +/* Generic timer counter frequency, in Hz */
> +uint64_t gt_cntfrq;
> };
>
> +static inline unsigned int gt_cntfrq_period_ns(ARMCPU *cpu)
> +{
> +/* XXX: Could include qemu/timer.h to get NANOSECONDS_PER_SECOND? */
> +const unsigned int ns_per_s = 1000 * 1000 * 1000;
> +return ns_per_s > cpu->gt_cntfrq ? ns_per_s / cpu->gt_cntfrq : 1;
> +}
Are you inlining this helper for performance reasons ?
C.
> void arm_cpu_post_init(Object *obj);
>
> uint64_t arm_cpu_mp_affinity(int idx, uint8_t clustersz);
> diff --git a/target/arm/helper.c b/target/arm/helper.c
> index 65c4441a3896..1cc0551081a0 100644
> --- a/target/arm/helper.c
> +++ b/target/arm/helper.c
> @@ -2409,7 +2409,9 @@ static CPAccessResult gt_stimer_access(CPUARMState *env,
>
> static uint64_t gt_get_countervalue(CPUARMState *env)
> {
> -return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) / GTIMER_SCALE;
> +ARMCPU *cpu = env_archcpu(env);
> +
> +return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) / gt_cntfrq_period_ns(cpu);
> }
>
> static void gt_recalc_timer(ARMCPU *cpu, int timeridx)
> @@ -2445,7 +2447,7 @@ static void gt_recalc_timer(ARMCPU *cpu, int timeridx)
> * set the timer for as far in the future as possible. When the
> * timer expires we will reset the timer for any remaining period.
> */
> -if (nexttick > INT64_MAX / GTIMER_SCALE) {
> +if (nexttick > INT64_MAX / gt_cntfrq_period_ns(cpu)) {
> timer_mod_ns(cpu->gt_timer[timeridx], INT64_MAX);
> } else {
> timer_mod(cpu->gt_timer[timeridx], nexttick);
> @@ -2874,11 +2876,13 @@ static const ARMCPRegInfo generic_timer_cp_reginfo[]
> = {
>
> static uint64_t gt_virt_cnt_read(CPUARMState *env, const ARMCPRegInfo *ri)
> {
> +ARMCPU *cpu = env_archcpu(env);
> +
> /* Currently we have no support for QEMUTimer in linux-user so we
> * can't call gt_get_countervalue(env), instead we directly
> * call the lower level functions.
> */
> -return cpu_get_clock() / GTIMER_SCALE;
> +return cpu_get_clock() / gt_cntfrq_period(cpu);
> }
>
> static const ARMCPRegInfo generic_timer_cp_reginfo[] = {
>
