linux-kernel - [PATCH] clocksource/drivers/riscv: Increase the clock source rating

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Message-Id: <20221228004444.61568-1-samuel@sholland.org>
Date:   Tue, 27 Dec 2022 18:44:44 -0600
From:   Samuel Holland <samuel@...lland.org>
To:     Palmer Dabbelt <palmer@...belt.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Prabhakar Lad <prabhakar.csengg@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: [PATCH] clocksource/drivers/riscv: Increase the clock source rating

RISC-V provides an architectural clock source via the time CSR. This
clock source exposes a 64-bit counter synchronized across all CPUs.
Because it is accessed using a CSR, it is much more efficient to read
than MMIO clock sources. For example, on the Allwinner D1, reading the
sun4i timer in a loop takes 131 cycles/iteration, while reading the
RISC-V time CSR takes only 5 cycles/iteration.

Adjust the RISC-V clock source rating so it is preferred over the
various platform-specific MMIO clock sources.

Signed-off-by: Samuel Holland <samuel@...lland.org>
---

 drivers/clocksource/timer-riscv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
index a0d66fabf073..55dad7965f43 100644
--- a/drivers/clocksource/timer-riscv.c
+++ b/drivers/clocksource/timer-riscv.c
@@ -73,7 +73,7 @@ static u64 notrace riscv_sched_clock(void)
 
 static struct clocksource riscv_clocksource = {
 	.name		= "riscv_clocksource",
-	.rating		= 300,
+	.rating		= 400,
 	.mask		= CLOCKSOURCE_MASK(64),
 	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
 	.read		= riscv_clocksource_rdtime,
-- 
2.37.4