linux-kernel - Re: [PATCH v2 10/10] clocksource/drivers/hyper-v: Move handling of STIMER0 interrupts

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Date:   Mon, 1 Mar 2021 19:44:40 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Michael Kelley <mikelley@...rosoft.com>, sthemmin@...rosoft.com,
        kys@...rosoft.com, wei.liu@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com, arnd@...db.de,
        linux-hyperv@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH v2 10/10] clocksource/drivers/hyper-v: Move handling of
 STIMER0 interrupts

On 01/03/2021 02:15, Michael Kelley wrote:
> STIMER0 interrupts are most naturally modeled as per-cpu IRQs. But
> because x86/x64 doesn't have per-cpu IRQs, the core STIMER0 interrupt
> handling machinery is done in code under arch/x86 and Linux IRQs are
> not used. Adding support for ARM64 means adding equivalent code
> using per-cpu IRQs under arch/arm64.
> 
> A better model is to treat per-cpu IRQs as the normal path (which it is
> for modern architectures), and the x86/x64 path as the exception. Do this
> by incorporating standard Linux per-cpu IRQ allocation into the main
> SITMER0 driver code, and bypass it in the x86/x64 exception case. For
> x86/x64, special case code is retained under arch/x86, but no STIMER0
> interrupt handling code is needed under arch/arm64.
> 
> No functional change.
> 
> Signed-off-by: Michael Kelley <mikelley@...rosoft.com>
> ---
>  arch/x86/hyperv/hv_init.c          |   2 +-
>  arch/x86/include/asm/mshyperv.h    |   4 -
>  arch/x86/kernel/cpu/mshyperv.c     |  10 +--
>  drivers/clocksource/hyperv_timer.c | 180 ++++++++++++++++++++++++++-----------
>  include/asm-generic/mshyperv.h     |   5 --
>  include/clocksource/hyperv_timer.h |   3 +-
>  6 files changed, 132 insertions(+), 72 deletions(-)
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 9af4f8a..9d10025 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -327,7 +327,7 @@ static void __init hv_stimer_setup_percpu_clockev(void)
>  	 * Ignore any errors in setting up stimer clockevents
>  	 * as we can run with the LAPIC timer as a fallback.
>  	 */
> -	(void)hv_stimer_alloc();
> +	(void)hv_stimer_alloc(false);
>  
>  	/*
>  	 * Still register the LAPIC timer, because the direct-mode STIMER is
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 5433312..6d4891b 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -31,10 +31,6 @@ static inline u64 hv_get_register(unsigned int reg)
>  
>  void hyperv_vector_handler(struct pt_regs *regs);
>  
> -static inline void hv_enable_stimer0_percpu_irq(int irq) {}
> -static inline void hv_disable_stimer0_percpu_irq(int irq) {}
> -
> -
>  #if IS_ENABLED(CONFIG_HYPERV)
>  extern int hyperv_init_cpuhp;
>  
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 41fd84a..cebed53 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -90,21 +90,17 @@ void hv_remove_vmbus_handler(void)
>  	set_irq_regs(old_regs);
>  }
>  
> -int hv_setup_stimer0_irq(int *irq, int *vector, void (*handler)(void))
> +/* For x86/x64, override weak placeholders in hyperv_timer.c */
> +void hv_setup_stimer0_handler(void (*handler)(void))
>  {
> -	*vector = HYPERV_STIMER0_VECTOR;
> -	*irq = -1;   /* Unused on x86/x64 */
>  	hv_stimer0_handler = handler;
> -	return 0;
>  }
> -EXPORT_SYMBOL_GPL(hv_setup_stimer0_irq);
>  
> -void hv_remove_stimer0_irq(int irq)
> +void hv_remove_stimer0_handler(void)
>  {
>  	/* We have no way to deallocate the interrupt gate */
>  	hv_stimer0_handler = NULL;
>  }
> -EXPORT_SYMBOL_GPL(hv_remove_stimer0_irq);
>  
>  void hv_setup_kexec_handler(void (*handler)(void))
>  {
> diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
> index cdb8e0c..b2bf5e5 100644
> --- a/drivers/clocksource/hyperv_timer.c
> +++ b/drivers/clocksource/hyperv_timer.c
> @@ -18,6 +18,9 @@
>  #include <linux/sched_clock.h>
>  #include <linux/mm.h>
>  #include <linux/cpuhotplug.h>
> +#include <linux/interrupt.h>
> +#include <linux/irq.h>
> +#include <linux/acpi.h>
>  #include <clocksource/hyperv_timer.h>
>  #include <asm/hyperv-tlfs.h>
>  #include <asm/mshyperv.h>
> @@ -43,14 +46,13 @@
>   */
>  static bool direct_mode_enabled;
>  
> -static int stimer0_irq;
> -static int stimer0_vector;
> +static int stimer0_irq = -1;
> +static long __percpu *stimer0_evt;

Why not

static DEFINE_PER_CPU(long, stimer0_evt);

no need of allocation /free ?






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