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SubjectRe: [Xen-devel] linux 4.4 Regression: 100% cpu usage on idle pv guest under Xen with single vcpu.
On 2015-12-02 15:55, David Vrabel wrote:
> On 28/11/15 15:47, Sander Eikelenboom wrote:
>> genirq: Flags mismatch irq 8. 00000000 (hvc_console) vs. 00000000
>> (rtc0)
>
> We shouldn't register an rtc_cmos device because its legacy irq
> conflicts with the irq needed for hvc0. For a multi VCPU guest irq 8
> is
> in use for the pv spinlocks and this gets requested first, preventing
> the rtc device from probing.
>
> Does this patch fix it for you?
>
> David

It does, thanks.

Reported-and-tested-by: Sander Eikelenboom <linux@eikelenboom.it>

--
Sander

> 8<--------------------
> x86: rtc_cmos platform device requires legacy irqs
>
> Adding the rtc platform device when there are no legacy irqs (no
> legacy PIC) causes a conflict with other devices that end up using the
> same irq number.
>
> In a single VCPU PV guest we should have:
>
> /proc/interrupts:
> CPU0
> 0: 4934 xen-percpu-virq timer0
> 1: 0 xen-percpu-ipi spinlock0
> 2: 0 xen-percpu-ipi resched0
> 3: 0 xen-percpu-ipi callfunc0
> 4: 0 xen-percpu-virq debug0
> 5: 0 xen-percpu-ipi callfuncsingle0
> 6: 0 xen-percpu-ipi irqwork0
> 7: 321 xen-dyn-event xenbus
> 8: 90 xen-dyn-event hvc_console
> ...
>
> But hvc_console cannot get its interrupt because it is already in use
> by rtc0 and the console does not work.
>
> genirq: Flags mismatch irq 8. 00000000 (hvc_console) vs. 00000000
> (rtc0)
>
> The rtc_cmos device requires a particular legacy irq so don't add it
> if there are no legacy irqs.
>
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> ---
> arch/x86/kernel/rtc.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c
> index cd96852..07c70f1 100644
> --- a/arch/x86/kernel/rtc.c
> +++ b/arch/x86/kernel/rtc.c
> @@ -14,6 +14,7 @@
> #include <asm/time.h>
> #include <asm/intel-mid.h>
> #include <asm/rtc.h>
> +#include <asm/i8259.h>
>
> #ifdef CONFIG_X86_32
> /*
> @@ -200,6 +201,10 @@ static __init int add_rtc_cmos(void)
> }
> #endif
>
> + /* RTC uses legacy IRQs. */
> + if (!nr_legacy_irqs())
> + return -ENODEV;
> +
> platform_device_register(&rtc_device);
> dev_info(&rtc_device.dev,
> "registered platform RTC device (no PNP device found)\n");


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