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

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Date:   Tue, 2 Mar 2021 01:40:37 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: RE: [PATCH v2 10/10] clocksource/drivers/hyper-v: Move handling of
 STIMER0 interrupts

From: Daniel Lezcano <daniel.lezcano@...aro.org> Sent: Monday, March 1, 2021 10:45 AM
> 
> 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 ?
> 

Indeed!  I'll make that simplification in v3 of the patch set.

Michael