[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH v2 2/2] xen/x86: ioapic: Bail out from timer_irq_works() as soon as possible
From: Julien Grall <jgrall@xxxxxxxxxx> Currently timer_irq_works() will wait the full 100ms before checking that pit0_ticks has been incremented at least 4 times. However, the bulk of the BIOS/platform should not have a buggy timer. So waiting for the full 100ms is a bit harsh. Rework the logic to only wait until 100ms passed or we saw more than 4 ticks. So now, in the good case, this will reduce the wait time to ~50ms. Take the opportunity to change the prototype of timer_irq_works() to return a bool rather than int (which was already acting as a bool because only 0/1 could be returned). Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx> --- Note that local_irq_restore() cannot be replaced with local_irq_disable() because the function is not consistently called with IRQs off. Changes in v2: - Return bool rather than int - Have a single return path - Use 'unsigned int' rather than 'unsigned long' for msec --- xen/arch/x86/io_apic.c | 39 ++++++++++++++++++++++++--------------- 1 file changed, 24 insertions(+), 15 deletions(-) diff --git a/xen/arch/x86/io_apic.c b/xen/arch/x86/io_apic.c index 238b6c1c2837..c89fbed8d675 100644 --- a/xen/arch/x86/io_apic.c +++ b/xen/arch/x86/io_apic.c @@ -1506,32 +1506,41 @@ static void __init setup_ioapic_ids_from_mpc(void) * - if this function detects that timer IRQs are defunct, then we fall * back to ISA timer IRQs */ -static int __init timer_irq_works(void) +static bool __init timer_irq_works(void) { unsigned long t1, flags; + /* Wait for maximum 10 ticks */ + unsigned int msec = (10 * 1000) / HZ; + bool works = false; if ( pit_irq_works ) - return 1; + return true; t1 = ACCESS_ONCE(pit0_ticks); local_save_flags(flags); local_irq_enable(); - /* Let ten ticks pass... */ - mdelay((10 * 1000) / HZ); - local_irq_restore(flags); - /* - * Expect a few ticks at least, to be sure some possible - * glue logic does not lock up after one or two first - * ticks in a non-ExtINT mode. Also the local APIC - * might have cached one ExtINT interrupt. Finally, at - * least one tick may be lost due to delays. - */ - if ( (ACCESS_ONCE(pit0_ticks) - t1) > 4 ) - return 1; + while ( msec-- ) + { + mdelay(1); + /* + * Expect a few ticks at least, to be sure some possible + * glue logic does not lock up after one or two first + * ticks in a non-ExtINT mode. Also the local APIC + * might have cached one ExtINT interrupt. Finally, at + * least one tick may be lost due to delays. + */ + if ( (ACCESS_ONCE(pit0_ticks) - t1) <= 4 ) + continue; - return 0; + works = true; + break; + } + + local_irq_restore(flags); + + return works; } /* -- 2.40.1
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