[RFC PATCH] apei/ghes: fix ghes_poll_func by registering in non-deferrable mode

Bhaskar Upadhaya
2019-12-18T07:04:19Z

Currently Linux register ghes_poll_func with TIMER_DEFERRABLE flag,
because of which it is serviced when the CPU eventually wakes up with a
subsequent non-deferrable timer and not at the configured polling interval.

For polling mode, the polling interval configured by firmware should not
be exceeded as per ACPI_6_3 spec[refer Table 18-394], So Timer need to
be configured in non-deferrable mode by removing TIMER_DEFERRABLE flag.
With NO_HZ enabled and timer callback being configured in non-deferrable
mode, timer callback will get called exactly after polling interval.

Impact of removing TIMER_DEFFERABLE flag
- With NO_HZ enabled, additional timer ticks and unnecessary wakeups of
the cpu happens exactly after polling interval.

- If polling interval is too small than polling function will be called
too frequently which may stall the cpu.

Signed-off-by: Bhaskar Upadhaya <bupadhaya@marvell.com>
---
drivers/acpi/apei/ghes.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
index 777f6f7122b4..c8f9230f69fb 100644
--- a/drivers/acpi/apei/ghes.c
+++ b/drivers/acpi/apei/ghes.c
@@ -1181,7 +1181,7 @@ static int ghes_probe(struct platform_device *ghes_dev)

switch (generic->notify.type) {
case ACPI_HEST_NOTIFY_POLLED:
- timer_setup(&ghes->timer, ghes_poll_func, TIMER_DEFERRABLE);
+ timer_setup(&ghes->timer, ghes_poll_func, 0);
ghes_add_timer(ghes);
break;
case ACPI_HEST_NOTIFY_EXTERNAL:
--
2.17.1