On Wed, 1 May 2024 09:16:33 +0100 Peter Hoyes <peter.ho...@arm.com> wrote:
Hi Peter, thanks for the change! > From: Peter Hoyes <peter.ho...@arm.com> > > Polling cntpct_el0 in a tight loop for delays is inefficient. > This is particularly apparent on Arm FVPs, which do not simulate > real time, meaning that a 1s sleep can take a couple of orders > of magnitude longer to execute in wall time. > > If running at EL2 or above (where CNTHCTL_EL2 is available), enable > the cntpct_el0 event stream temporarily and use wfe to implement > the delay more efficiently. The event period is chosen as a > trade-off between efficiency and the fact that Arm FVPs do not > typically simulate real time. > > This is only implemented for Armv8 boards, where an architectural > timer exists, and only enabled by default for the ARCH_VEXPRESS64 > board family. I think total_compute would benefit from this change as well, but this needs some testing and can easily be a separate patch. > Signed-off-by: Peter Hoyes <peter.ho...@arm.com> Reviewed-by: Andre Przywara <andre.przyw...@arm.com> Cheers, Andre > --- > arch/arm/cpu/armv8/Kconfig | 8 ++++++++ > arch/arm/cpu/armv8/generic_timer.c | 27 +++++++++++++++++++++++++++ > arch/arm/include/asm/system.h | 6 ++++-- > 3 files changed, 39 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/cpu/armv8/Kconfig b/arch/arm/cpu/armv8/Kconfig > index 9f0fb369f7..199335cd60 100644 > --- a/arch/arm/cpu/armv8/Kconfig > +++ b/arch/arm/cpu/armv8/Kconfig > @@ -191,6 +191,14 @@ config ARMV8_EA_EL3_FIRST > Exception handling at all exception levels for External Abort > and SError interrupt exception are taken in EL3. > > +config ARMV8_UDELAY_EVENT_STREAM > + bool "Use the event stream for udelay" > + default y if ARCH_VEXPRESS64 > + help > + Use the event stream provided by the AArch64 architectural > timer for > + delays. This is more efficient than the default polling > + implementation. > + > menuconfig ARMV8_CRYPTO > bool "ARM64 Accelerated Cryptographic Algorithms" > > diff --git a/arch/arm/cpu/armv8/generic_timer.c > b/arch/arm/cpu/armv8/generic_timer.c index 8f83372cbc..e18b5c8187 100644 > --- a/arch/arm/cpu/armv8/generic_timer.c > +++ b/arch/arm/cpu/armv8/generic_timer.c > @@ -115,3 +115,30 @@ ulong timer_get_boot_us(void) > > return val / get_tbclk(); > } > + > +#if CONFIG_IS_ENABLED(ARMV8_UDELAY_EVENT_STREAM) > +void __udelay(unsigned long usec) > +{ > + u64 target = get_ticks() + usec_to_tick(usec); > + > + /* At EL2 or above, use the event stream to avoid polling > CNTPCT_EL0 so often */ > + if (current_el() >= 2) { > + u32 cnthctl_val; > + const u8 event_period = 0x7; > + > + asm volatile("mrs %0, cnthctl_el2" : "=r" > (cnthctl_val)); > + asm volatile("msr cnthctl_el2, %0" : : "r" > + (cnthctl_val | CNTHCTL_EL2_EVNT_EN | > CNTHCTL_EL2_EVNT_I(event_period))); + > + while (get_ticks() + (1ULL << event_period) <= target) > + wfe(); > + > + /* Reset the event stream */ > + asm volatile("msr cnthctl_el2, %0" : : "r" > (cnthctl_val)); > + } > + > + /* Fall back to polling CNTPCT_EL0 */ > + while (get_ticks() <= target) > + ; > +} > +#endif > diff --git a/arch/arm/include/asm/system.h > b/arch/arm/include/asm/system.h index 51123c2968..7e30cac32a 100644 > --- a/arch/arm/include/asm/system.h > +++ b/arch/arm/include/asm/system.h > @@ -69,8 +69,10 @@ > /* > * CNTHCTL_EL2 bits definitions > */ > -#define CNTHCTL_EL2_EL1PCEN_EN (1 << 1) /* Physical timer regs > accessible */ -#define CNTHCTL_EL2_EL1PCTEN_EN (1 << 0) /* > Physical counter accessible */ +#define CNTHCTL_EL2_EVNT_EN > BIT(2) /* Enable the event stream */ +#define > CNTHCTL_EL2_EVNT_I(val) ((val) << 4) /* Event stream trigger bits > */ +#define CNTHCTL_EL2_EL1PCEN_EN (1 << 1) /* Physical > timer regs accessible */ +#define CNTHCTL_EL2_EL1PCTEN_EN (1 << > 0) /* Physical counter accessible */ /* > * HCR_EL2 bits definitions