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

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Date:   Thu, 25 Feb 2021 18:56:00 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     Boqun Feng <boqun.feng@...il.com>
CC:     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>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "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 10/10] clocksource/drivers/hyper-v: Move handling of
 STIMER0 interrupts

From: Boqun Feng <boqun.feng@...il.com> Sent: Monday, February 22, 2021 10:47 PM
> 
> On Wed, Jan 27, 2021 at 12:23:45PM -0800, 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 | 170 +++++++++++++++++++++++++------------
> >  include/asm-generic/mshyperv.h     |   5 --
> >  include/clocksource/hyperv_timer.h |   3 +-
> >  6 files changed, 123 insertions(+), 71 deletions(-)
> >

[snip]

> > +static void hv_remove_stimer0_irq(void)
> > +{
> > +	if (stimer0_irq != -1) {
> > +		free_percpu_irq(stimer0_irq, stimer0_evt);
> > +		free_percpu(stimer0_evt);
> > +		acpi_unregister_gsi(stimer0_irq);
> > +		stimer0_irq = -1;
> > +	}
> 
> I think we need:
> 
> 	else {
> 		hv_remove_stimer0_handler();
> 	}
> 
> here?
> 
> Because previously, on x86 we set hv_stimer0_handler to NULL in
> hv_remove_stimer0_irq(), however, this patch doesn't keep this behavior
> any more.
> 
> Thoughts?
> 
> Regards,
> Boqun

Yes, agreed.  Will fix this in v2.

Michael