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From: Conor Dooley <conor@kernel.org>
To: Jisheng Zhang <jszhang@kernel.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>, Guo Ren <guoren@kernel.org>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	Emil Renner Berthing <emil.renner.berthing@canonical.com>
Subject: Re: [PATCH v2 1/2] riscv: errata: thead: use riscv_nonstd_cache_ops for CMO
Date: Mon, 2 Oct 2023 11:55:31 +0100	[thread overview]
Message-ID: <20231002-angles-utopia-6c6c7b18231e@spud> (raw)
In-Reply-To: <20231001103433.3187-2-jszhang@kernel.org>


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On Sun, Oct 01, 2023 at 06:34:32PM +0800, Jisheng Zhang wrote:
> Previously, we use alternative mechanism to dynamically patch
> the CMO operations for THEAD C906/C910 during boot for performance
> reason. But as pointed out by Arnd, "there is already a significant
> cost in accessing the invalidated cache lines afterwards, which is
> likely going to be much higher than the cost of an indirect branch".
> And indeed, there's no performance difference with GMAC and EMMC per
> my test on Sipeed Lichee Pi 4A board.
> 
> Use riscv_nonstd_cache_ops for THEAD C906/C910 CMO to simplify
> the alternative code, and to acchieve Arnd's goal -- "I think
> moving the THEAD ops at the same level as all nonstandard operations
> makes sense, but I'd still leave CMO as an explicit fast path that
> avoids the indirect branch. This seems like the right thing to do both
> for readability and for platforms on which the indirect branch has a
> noticeable overhead."
> 
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> Tested-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

Thanks,
Conor.

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WARNING: multiple messages have this Message-ID (diff)
From: Conor Dooley <conor@kernel.org>
To: Jisheng Zhang <jszhang@kernel.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>, Guo Ren <guoren@kernel.org>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	Emil Renner Berthing <emil.renner.berthing@canonical.com>
Subject: Re: [PATCH v2 1/2] riscv: errata: thead: use riscv_nonstd_cache_ops for CMO
Date: Mon, 2 Oct 2023 11:55:31 +0100	[thread overview]
Message-ID: <20231002-angles-utopia-6c6c7b18231e@spud> (raw)
In-Reply-To: <20231001103433.3187-2-jszhang@kernel.org>

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On Sun, Oct 01, 2023 at 06:34:32PM +0800, Jisheng Zhang wrote:
> Previously, we use alternative mechanism to dynamically patch
> the CMO operations for THEAD C906/C910 during boot for performance
> reason. But as pointed out by Arnd, "there is already a significant
> cost in accessing the invalidated cache lines afterwards, which is
> likely going to be much higher than the cost of an indirect branch".
> And indeed, there's no performance difference with GMAC and EMMC per
> my test on Sipeed Lichee Pi 4A board.
> 
> Use riscv_nonstd_cache_ops for THEAD C906/C910 CMO to simplify
> the alternative code, and to acchieve Arnd's goal -- "I think
> moving the THEAD ops at the same level as all nonstandard operations
> makes sense, but I'd still leave CMO as an explicit fast path that
> avoids the indirect branch. This seems like the right thing to do both
> for readability and for platforms on which the indirect branch has a
> noticeable overhead."
> 
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> Tested-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

Thanks,
Conor.

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  reply	other threads:[~2023-10-02 10:55 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-10-01 10:34 [PATCH v2 0/2] riscv: errata: thead: use riscv_nonstd_cache_ops for CMO Jisheng Zhang
2023-10-01 10:34 ` Jisheng Zhang
2023-10-01 10:34 ` [PATCH v2 1/2] " Jisheng Zhang
2023-10-01 10:34   ` Jisheng Zhang
2023-10-02 10:55   ` Conor Dooley [this message]
2023-10-02 10:55     ` Conor Dooley
2023-10-06  2:43   ` Guo Ren
2023-10-06  2:43     ` Guo Ren
2023-10-12 12:43   ` Clément Léger
2023-10-12 12:43     ` Clément Léger
2023-10-12 14:17     ` Jisheng Zhang
2023-10-12 14:17       ` Jisheng Zhang
2023-10-01 10:34 ` [PATCH v2 2/2] riscv: errata: thead: use pa based instructions " Jisheng Zhang
2023-10-01 10:34   ` Jisheng Zhang
2023-10-08 10:11   ` Guo Ren
2023-10-08 10:11     ` Guo Ren
2023-10-06  2:48 ` [PATCH v2 0/2] riscv: errata: thead: use riscv_nonstd_cache_ops " Guo Ren
2023-10-06  2:48   ` Guo Ren

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