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[193.12.47.89]) by smtp.gmail.com with ESMTPSA id p28sm1529335lfo.79.2022.01.26.15.12.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 26 Jan 2022 15:12:52 -0800 (PST) From: Tobias Waldekranz To: davem@davemloft.net, kuba@kernel.org Cc: netdev@vger.kernel.org, Andrew Lunn , Vivien Didelot , Florian Fainelli , Vladimir Oltean , linux-kernel@vger.kernel.org Subject: [PATCH net-next 1/2] net: dsa: mv88e6xxx: Improve performance of busy bit polling Date: Thu, 27 Jan 2022 00:12:38 +0100 Message-Id: <20220126231239.1443128-2-tobias@waldekranz.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220126231239.1443128-1-tobias@waldekranz.com> References: <20220126231239.1443128-1-tobias@waldekranz.com> MIME-Version: 1.0 Organization: Westermo Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Avoid a long delay when a busy bit is still set and has to be polled again. Measurements on a system with 2 Opals (6097F) and one Agate (6352) show that even with this much tighter loop, we have about a 50% chance of the bit being cleared on the first poll, all other accesses see the bit being cleared on the second poll. On a standard MDIO bus running MDC at 2.5MHz, a single access with 32 bits of preamble plus 32 bits of data takes 64*(1/2.5MHz) = 25.6us. This means that mv88e6xxx_smi_direct_wait took 26us + CPU overhead in the fast scenario, but 26us + 1500us + 26us + CPU overhead in the slow case - bringing the average close to 1ms. With this change in place, the slow case is closer to 2*26us + CPU overhead, with the average well below 100us - a 10x improvement. This translates to real-world winnings. On a 3-chip 20-port system, the modprobe time drops by 88%: Before: root@coronet:~# time modprobe mv88e6xxx real 0m 15.99s user 0m 0.00s sys 0m 1.52s After: root@coronet:~# time modprobe mv88e6xxx real 0m 2.21s user 0m 0.00s sys 0m 1.54s Signed-off-by: Tobias Waldekranz --- drivers/net/dsa/mv88e6xxx/chip.c | 8 ++++---- drivers/net/dsa/mv88e6xxx/smi.c | 8 ++++---- 2 files changed, 8 insertions(+), 8 deletions(-) diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c index 58ca684d73f7..3566617143cf 100644 --- a/drivers/net/dsa/mv88e6xxx/chip.c +++ b/drivers/net/dsa/mv88e6xxx/chip.c @@ -86,12 +86,12 @@ int mv88e6xxx_write(struct mv88e6xxx_chip *chip, int addr, int reg, u16 val) int mv88e6xxx_wait_mask(struct mv88e6xxx_chip *chip, int addr, int reg, u16 mask, u16 val) { + const unsigned long timeout = jiffies + msecs_to_jiffies(50); u16 data; int err; - int i; /* There's no bus specific operation to wait for a mask */ - for (i = 0; i < 16; i++) { + do { err = mv88e6xxx_read(chip, addr, reg, &data); if (err) return err; @@ -99,8 +99,8 @@ int mv88e6xxx_wait_mask(struct mv88e6xxx_chip *chip, int addr, int reg, if ((data & mask) == val) return 0; - usleep_range(1000, 2000); - } + cpu_relax(); + } while (time_before(jiffies, timeout)); dev_err(chip->dev, "Timeout while waiting for switch\n"); return -ETIMEDOUT; diff --git a/drivers/net/dsa/mv88e6xxx/smi.c b/drivers/net/dsa/mv88e6xxx/smi.c index 282fe08db050..a59f32243e08 100644 --- a/drivers/net/dsa/mv88e6xxx/smi.c +++ b/drivers/net/dsa/mv88e6xxx/smi.c @@ -55,11 +55,11 @@ static int mv88e6xxx_smi_direct_write(struct mv88e6xxx_chip *chip, static int mv88e6xxx_smi_direct_wait(struct mv88e6xxx_chip *chip, int dev, int reg, int bit, int val) { + const unsigned long timeout = jiffies + msecs_to_jiffies(50); u16 data; int err; - int i; - for (i = 0; i < 16; i++) { + do { err = mv88e6xxx_smi_direct_read(chip, dev, reg, &data); if (err) return err; @@ -67,8 +67,8 @@ static int mv88e6xxx_smi_direct_wait(struct mv88e6xxx_chip *chip, if (!!(data & BIT(bit)) == !!val) return 0; - usleep_range(1000, 2000); - } + cpu_relax(); + } while (time_before(jiffies, timeout)); return -ETIMEDOUT; } -- 2.25.1