Hi Jan,
On 07/09/2023 15:28, Jan Beulich wrote:
On 18.08.2023 15:44, Julien Grall wrote:
From: Julien Grall <[email protected]>
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.
Signed-off-by: Julien Grall <[email protected]>
In principle this is all fine. There's a secondary aspect though which
may call for a slight rework of the patch.
--- a/xen/arch/x86/io_apic.c
+++ b/xen/arch/x86/io_apic.c
@@ -1509,6 +1509,8 @@ static void __init setup_ioapic_ids_from_mpc(void)
static int __init timer_irq_works(void)
{
unsigned long t1, flags;
+ /* Wait for maximum 10 ticks */
+ unsigned long msec = (10 * 1000) / HZ;
(Minor remark: I don't think this needs to be unsigned long; unsigned
in will suffice.)
You are right. I can switch to unsigned int.
@@ -1517,19 +1519,25 @@ static int __init timer_irq_works(void)
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 )
+ 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;
+
+ local_irq_restore(flags);
return 1;
+ }
+
+ local_irq_restore(flags);
return 0;
}
While Andrew has a patch pending (not sure why it didn't go in yet)
to simplify local_irq_restore(), and while further it shouldn't really
need using here (local_irq_disable() ought to be fine)
Skimming through the code, the last call of timer_irq_works() in
check_timer() happens after the interrupts masking state have been restored:
local_irq_restore(flags);
if ( timer_irq_works() )
...
So I think timer_irq_works() can be called with interrupts enabled and
therefore we can't use local_irq_disable().
I can see that
you don't want to make such an adjustment here. But then I'd prefer if
we got away with just a single instance, adjusting the final return
statement accordingly (easiest would likely be to go from the value of
"msec").
I was thinking to use 'msec > 0' as a condition to determine if the test
passed. However, it would consider a failure if it tooks 10ms for the
test to pass.
I will see if I can rework the loop.
Cheers,
--
Julien Grall
