linux-kernel - [PATCH 1/1] char: hpet: Remove unused local variable 'm' in hpet

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Date:   Thu, 15 Apr 2021 22:24:04 +0800
From:   Zhen Lei <thunder.leizhen@...wei.com>
To:     Clemens Ladisch <clemens@...isch.de>,
        Arnd Bergmann <arnd@...db.de>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
CC:     Zhen Lei <thunder.leizhen@...wei.com>,
        Nils Carlson <nils.carlson@...csson.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 1/1] char: hpet: Remove unused local variable 'm' in hpet_interrupt()

Commit 273ef9509b79 ("drivers/char/hpet.c: fix periodic-emulation for
delayed interrupt") removed the reference to local variable 'm', but
forgot to remove the definition and assignment of it. Due to
read_counter() indirectly calls "read barrier", the performance is
slightly degraded.

Since the following comments give some description based on 'm', so move
the assignment of 'm' into it.

Fixes: 273ef9509b79 ("drivers/char/hpet.c: fix periodic-emulation for delayed interrupt")
Reported-by: Hulk Robot <hulkci@...wei.com>
Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
---
 drivers/char/hpet.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
index ed3b7dab678dbd1..46950a0cda181a1 100644
--- a/drivers/char/hpet.c
+++ b/drivers/char/hpet.c
@@ -156,14 +156,16 @@ static irqreturn_t hpet_interrupt(int irq, void *data)
 	 * This has the effect of treating non-periodic like periodic.
 	 */
 	if ((devp->hd_flags & (HPET_IE | HPET_PERIODIC)) == HPET_IE) {
-		unsigned long m, t, mc, base, k;
+		unsigned long t, mc, base, k;
 		struct hpet __iomem *hpet = devp->hd_hpet;
 		struct hpets *hpetp = devp->hd_hpets;
 
 		t = devp->hd_ireqfreq;
-		m = read_counter(&devp->hd_timer->hpet_compare);
 		mc = read_counter(&hpet->hpet_mc);
-		/* The time for the next interrupt would logically be t + m,
+		/*
+		 * m = read_counter(&devp->hd_timer->hpet_compare);
+		 *
+		 * The time for the next interrupt would logically be t + m,
 		 * however, if we are very unlucky and the interrupt is delayed
 		 * for longer than t then we will completely miss the next
 		 * interrupt if we set t + m and an application will hang.
-- 
2.26.0.106.g9fadedd