linux-kernel - [PATCH]optimize error handling in tick_check_new

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Message-ID: <20160727120609.GA3773@gauravjindalubtnb.del.spreadtrum.com>
Date:	Wed, 27 Jul 2016 12:06:17 +0000
From:	"Gaurav Jindal (Gaurav Jindal)" <Gaurav.Jindal@...eadtrum.com>
To:	"tglx@...utronix.de" <tglx@...utronix.de>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Sanjeev Yadav (Sanjeev Kumar Yadav)" <Sanjeev.Yadav@...eadtrum.com>
Subject: [PATCH]optimize error handling in tick_check_new_device

In the function tick_check_new_device, module error is handled after checking
if the newdev should go as broadcast-installation device in the functions
tick_check_percpu and tick_check_preferred. In case the try_module_get returns
false, the above 2 calls are extra thus wasting CPU cycles.

Shifting the try_module_get as first error handling saves CPU cycles when there
is nothing to do in case of module related error.

Signed-off-by:Gaurav Jindal<gaurav.jindal@...eadtrum.com>
Co-developed-by:Sanjeev Yadav<sanjeev.yadav@...eadtrum.com>

---

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 4fcd99e..23faf4a 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -307,6 +307,9 @@ void tick_check_new_device(struct clock_event_device *newdev)
 	td = &per_cpu(tick_cpu_device, cpu);
 	curdev = td->evtdev;

+	if (!try_module_get(newdev->owner))
+		return;
+
 	/* cpu local device ? */
 	if (!tick_check_percpu(curdev, newdev, cpu))
 		goto out_bc;
@@ -315,8 +318,6 @@ void tick_check_new_device(struct clock_event_device *newdev)
 	if (!tick_check_preferred(curdev, newdev))
 		goto out_bc;

-	if (!try_module_get(newdev->owner))
-		return;

 	/*
 	 * Replace the eventually existing device by the new