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From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Barry Song <21cnbao@gmail.com>
Cc: maz@kernel.org, tglx@linutronix.de, will@kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, linuxarm@huawei.com,
	Barry Song <song.bao.hua@hisilicon.com>
Subject: Re: [PATCH] irqchip/gic-v3: use dsb(ishst) to synchronize data to smp before issuing ipi
Date: Sun, 20 Feb 2022 15:04:18 +0000	[thread overview]
Message-ID: <YhJYct7aW0kGXNXp@shell.armlinux.org.uk> (raw)
In-Reply-To: <20220218215549.4274-1-song.bao.hua@hisilicon.com>

On Sat, Feb 19, 2022 at 05:55:49AM +0800, Barry Song wrote:
> dsb(ishst) should be enough here as we only need to guarantee the
> visibility of data to other CPUs in smp inner domain before we
> send the ipi.
> 
> Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
> ---
>  drivers/irqchip/irq-gic-v3.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index 5e935d97207d..0efe1a9a9f3b 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -1211,7 +1211,7 @@ static void gic_ipi_send_mask(struct irq_data *d, const struct cpumask *mask)
>  	 * Ensure that stores to Normal memory are visible to the
>  	 * other CPUs before issuing the IPI.
>  	 */
> -	wmb();
> +	dsb(ishst);

On ARM, wmb() is a dsb(st) followed by other operations which may
include a sync operation at the L2 cache, and SoC specific barriers
for the bus. Hopefully, nothing will break if the sledge hammer is
replaced by the tack hammer.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

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WARNING: multiple messages have this Message-ID (diff)
From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Barry Song <21cnbao@gmail.com>
Cc: maz@kernel.org, tglx@linutronix.de, will@kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, linuxarm@huawei.com,
	Barry Song <song.bao.hua@hisilicon.com>
Subject: Re: [PATCH] irqchip/gic-v3: use dsb(ishst) to synchronize data to smp before issuing ipi
Date: Sun, 20 Feb 2022 15:04:18 +0000	[thread overview]
Message-ID: <YhJYct7aW0kGXNXp@shell.armlinux.org.uk> (raw)
In-Reply-To: <20220218215549.4274-1-song.bao.hua@hisilicon.com>

On Sat, Feb 19, 2022 at 05:55:49AM +0800, Barry Song wrote:
> dsb(ishst) should be enough here as we only need to guarantee the
> visibility of data to other CPUs in smp inner domain before we
> send the ipi.
> 
> Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
> ---
>  drivers/irqchip/irq-gic-v3.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index 5e935d97207d..0efe1a9a9f3b 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -1211,7 +1211,7 @@ static void gic_ipi_send_mask(struct irq_data *d, const struct cpumask *mask)
>  	 * Ensure that stores to Normal memory are visible to the
>  	 * other CPUs before issuing the IPI.
>  	 */
> -	wmb();
> +	dsb(ishst);

On ARM, wmb() is a dsb(st) followed by other operations which may
include a sync operation at the L2 cache, and SoC specific barriers
for the bus. Hopefully, nothing will break if the sledge hammer is
replaced by the tack hammer.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

  parent reply	other threads:[~2022-02-20 15:07 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-18 21:55 [PATCH] irqchip/gic-v3: use dsb(ishst) to synchronize data to smp before issuing ipi Barry Song
2022-02-18 21:55 ` Barry Song
2022-02-19  9:56 ` Marc Zyngier
2022-02-19  9:56   ` Marc Zyngier
2022-02-19 23:46   ` Barry Song
2022-02-19 23:46     ` Barry Song
2022-02-20  1:33     ` Barry Song
2022-02-20  1:33       ` Barry Song
2022-02-20 13:30   ` Ard Biesheuvel
2022-02-20 13:30     ` Ard Biesheuvel
2022-02-20 15:04     ` Marc Zyngier
2022-02-20 15:04       ` Marc Zyngier
2022-02-20 15:05     ` Russell King (Oracle)
2022-02-20 15:05       ` Russell King (Oracle)
2022-02-20 20:09       ` Barry Song
2022-02-20 20:09         ` Barry Song
2022-02-20 15:04 ` Russell King (Oracle) [this message]
2022-02-20 15:04   ` Russell King (Oracle)
2022-02-20 15:21   ` Marc Zyngier
2022-02-20 15:21     ` Marc Zyngier
2022-02-20 20:20     ` Barry Song
2022-02-20 20:20       ` Barry Song

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