| Message ID | 1341566422-20368-5-git-send-email-marc.zyngier@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Marc, On 07/06/2012 05:20 AM, Marc Zyngier wrote: > In an environment supporting virtualization (KVM), the virtual timer > is reserved to the guests, while we rely on the physical timer for > the host. > > For this, we need to: > - switch the host CPUs from the virtual timer to the physical one > - provide an interrupt handler that is called by the virtual > timer's interrupt handler. > > The new function arch_timer_switch_to_phys() performs this task. It might be useful to CC the KVM mailing list to get their feedback. I feel like it's hard to give useful feedback without the context of the calling code. If the calling code is some kind of virtual clockchip, then could you use the existing clock event distribution mechanism rather than the custom hook? [...] > diff --git a/arch/arm/kernel/arch_timer.c b/arch/arm/kernel/arch_timer.c > index 4473f66..1bb632a 100644 > --- a/arch/arm/kernel/arch_timer.c > +++ b/arch/arm/kernel/arch_timer.c > @@ -50,6 +50,8 @@ struct arch_timer_reg_ops { > > static struct arch_timer_reg_ops __percpu **arch_timer_reg_ops; > > +static irq_handler_t arch_timer_virt_external_handler; > + > /* > * Architected system timer support. > */ > @@ -204,6 +206,19 @@ static irqreturn_t arch_timer_handler(int irq, void *dev_id) > > static irqreturn_t arch_timer_virt_handler(int irq, void *dev_id) > { > + if (arch_timer_virt_external_handler) { > + unsigned long ctrl; > + > + ctrl = arch_timer_virt_reg_read(ARCH_TIMER_REG_CTRL); > + if (ctrl & ARCH_TIMER_CTRL_IT_STAT) { > + ctrl |= ARCH_TIMER_CTRL_IT_MASK; > + arch_timer_virt_reg_write(ARCH_TIMER_REG_CTRL, ctrl); > + return arch_timer_virt_external_handler(irq, NULL); > + } > + > + return IRQ_NONE; > + } > + > return arch_timer_handler(irq, dev_id); > } Perhaps you could avoid some code duplication by calling arch_timer_handler at the beginning, stashing its return value, calling the external hook if it's defined, then returning whichever return value is appropriate. > > @@ -509,3 +524,37 @@ int __init arch_timer_sched_clock_init(void) > setup_sched_clock(arch_counter_get_cnt32, 32, arch_timer_rate); > return 0; > } > + > +static void arch_timer_switch_cpu_to_phys(void *dummy) > +{ > + u32 cvall, cvalh, val; > + > + pr_info("Switching CPU%d to physical timer\n", smp_processor_id()); > + > + asm volatile("mrrc p15, 3, %0, %1, c14 \n" /* Read CNTV_CVAL */ > + "mcrr p15, 2, %0, %1, c14 \n" /* Write CNTP_CVAL */ > + : "=r" (cvall), "=r" (cvalh)); I take it you don't use the easily readable helpers here because you're afraid of losing a few ticks? That makes me wonder if the mrc/mcr/mrrc/mcrr helpers could be expanded and improved to make them usable under these circumstances. > + > + isb(); > + (Trailing whitespace) > + val = arch_timer_virt_reg_read(ARCH_TIMER_REG_CTRL); > + arch_timer_virt_reg_write(ARCH_TIMER_REG_CTRL, > + val & ~ARCH_TIMER_CTRL_ENABLE); > + arch_timer_phys_reg_write(ARCH_TIMER_REG_CTRL, val); > + *__this_cpu_ptr(arch_timer_reg_ops) = &arch_timer_phys_ops; > +} > + > +void arch_timer_switch_to_phys(irq_handler_t handler) > +{ > + int cpu; > + > + if (!arch_timer_use_virtual) > + return; What will call this function? Won't it want to know the call failed? > + > + for_each_online_cpu(cpu) > + smp_call_function_single(cpu, arch_timer_switch_cpu_to_phys, > + NULL, 1); > + > + arch_timer_use_virtual = false; > + arch_timer_virt_external_handler = handler; > +} Thanks, Christopher
diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h index 72c6822..7cd1e27 100644 --- a/arch/arm/include/asm/arch_timer.h +++ b/arch/arm/include/asm/arch_timer.h @@ -2,11 +2,13 @@ #define __ASMARM_ARCH_TIMER_H #include <linux/clocksource.h> +#include <linux/interrupt.h> #ifdef CONFIG_ARM_ARCH_TIMER int arch_timer_of_register(void); int arch_timer_sched_clock_init(void); struct timecounter *arch_timer_get_timecounter(void); +void arch_timer_switch_to_phys(irq_handler_t); #else static inline int arch_timer_of_register(void) { @@ -22,6 +24,10 @@ static inline struct timecounter *arch_timer_get_timecounter(void) { return NULL; } + +static inline void arch_timer_switch_to_phys(irq_handler_t handler) +{ +} #endif #endif diff --git a/arch/arm/kernel/arch_timer.c b/arch/arm/kernel/arch_timer.c index 4473f66..1bb632a 100644 --- a/arch/arm/kernel/arch_timer.c +++ b/arch/arm/kernel/arch_timer.c @@ -50,6 +50,8 @@ struct arch_timer_reg_ops { static struct arch_timer_reg_ops __percpu **arch_timer_reg_ops; +static irq_handler_t arch_timer_virt_external_handler; + /* * Architected system timer support. */ @@ -204,6 +206,19 @@ static irqreturn_t arch_timer_handler(int irq, void *dev_id) static irqreturn_t arch_timer_virt_handler(int irq, void *dev_id) { + if (arch_timer_virt_external_handler) { + unsigned long ctrl; + + ctrl = arch_timer_virt_reg_read(ARCH_TIMER_REG_CTRL); + if (ctrl & ARCH_TIMER_CTRL_IT_STAT) { + ctrl |= ARCH_TIMER_CTRL_IT_MASK; + arch_timer_virt_reg_write(ARCH_TIMER_REG_CTRL, ctrl); + return arch_timer_virt_external_handler(irq, NULL); + } + + return IRQ_NONE; + } + return arch_timer_handler(irq, dev_id); } @@ -509,3 +524,37 @@ int __init arch_timer_sched_clock_init(void) setup_sched_clock(arch_counter_get_cnt32, 32, arch_timer_rate); return 0; } + +static void arch_timer_switch_cpu_to_phys(void *dummy) +{ + u32 cvall, cvalh, val; + + pr_info("Switching CPU%d to physical timer\n", smp_processor_id()); + + asm volatile("mrrc p15, 3, %0, %1, c14 \n" /* Read CNTV_CVAL */ + "mcrr p15, 2, %0, %1, c14 \n" /* Write CNTP_CVAL */ + : "=r" (cvall), "=r" (cvalh)); + + isb(); + + val = arch_timer_virt_reg_read(ARCH_TIMER_REG_CTRL); + arch_timer_virt_reg_write(ARCH_TIMER_REG_CTRL, + val & ~ARCH_TIMER_CTRL_ENABLE); + arch_timer_phys_reg_write(ARCH_TIMER_REG_CTRL, val); + *__this_cpu_ptr(arch_timer_reg_ops) = &arch_timer_phys_ops; +} + +void arch_timer_switch_to_phys(irq_handler_t handler) +{ + int cpu; + + if (!arch_timer_use_virtual) + return; + + for_each_online_cpu(cpu) + smp_call_function_single(cpu, arch_timer_switch_cpu_to_phys, + NULL, 1); + + arch_timer_use_virtual = false; + arch_timer_virt_external_handler = handler; +}
In an environment supporting virtualization (KVM), the virtual timer is reserved to the guests, while we rely on the physical timer for the host. For this, we need to: - switch the host CPUs from the virtual timer to the physical one - provide an interrupt handler that is called by the virtual timer's interrupt handler. The new function arch_timer_switch_to_phys() performs this task. Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> --- arch/arm/include/asm/arch_timer.h | 6 +++++ arch/arm/kernel/arch_timer.c | 49 +++++++++++++++++++++++++++++++++++++ 2 files changed, 55 insertions(+)