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

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Date:   Tue, 17 Dec 2019 23:03:38 -0800
From:   Bhaskar Upadhaya <bupadhaya@...vell.com>
To:     <linux-kernel@...r.kernel.org>, <linux-acpi@...r.kernel.org>,
        <linux-edac@...r.kernel.org>, <lenb@...nel.org>,
        <rafael@...nel.org>
CC:     <gkulkarni@...vell.com>, <rrichter@...vell.com>,
        <bhaskar.upadhaya.linux@...il.com>,
        Bhaskar Upadhaya <bupadhaya@...vell.com>
Subject: [RFC PATCH] apei/ghes: fix ghes_poll_func by registering in non-deferrable mode

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@...vell.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