linux-kernel - [PATCH] ipmi_si_intf: use usleep_range() instead of busy looping

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Date:   Tue, 9 Jul 2019 14:06:43 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Corey Minyard <minyard@....org>
Cc:     openipmi-developer@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: [PATCH] ipmi_si_intf: use usleep_range() instead of busy looping

ipmi_thread() uses back-to-back schedule() to poll for command
completion which, on some machines, can push up CPU consumption and
heavily tax the scheduler locks leading to noticeable overall
performance degradation.

This patch replaces schedule() with usleep_range(100, 200).  This
allows the sensor readings to finish resonably fast and the cpu
consumption of the kthread is kept under several percents of a core.

Signed-off-by: Tejun Heo <tj@...nel.org>
---
 drivers/char/ipmi/ipmi_si_intf.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/ipmi/ipmi_si_intf.c b/drivers/char/ipmi/ipmi_si_intf.c
index f124a2d2bb9f..2143e3c10623 100644
--- a/drivers/char/ipmi/ipmi_si_intf.c
+++ b/drivers/char/ipmi/ipmi_si_intf.c
@@ -1010,7 +1010,7 @@ static int ipmi_thread(void *data)
 		if (smi_result == SI_SM_CALL_WITHOUT_DELAY)
 			; /* do nothing */
 		else if (smi_result == SI_SM_CALL_WITH_DELAY && busy_wait)
-			schedule();
+			usleep_range(100, 200);
 		else if (smi_result == SI_SM_IDLE) {
 			if (atomic_read(&smi_info->need_watch)) {
 				schedule_timeout_interruptible(100);