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 v3 1/2] riscv: errata: thead: use riscv_nonstd_cache_ops for CMO
Date: Thu, 12 Oct 2023 15:36:53 +0100 [thread overview]
Message-ID: <20231012-pranker-usage-09a85a36356f@spud> (raw)
In-Reply-To: <20231012141456.4078-2-jszhang@kernel.org>
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On Thu, Oct 12, 2023 at 10:14:55PM +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>
From v2:
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 v3 1/2] riscv: errata: thead: use riscv_nonstd_cache_ops for CMO
Date: Thu, 12 Oct 2023 15:36:53 +0100 [thread overview]
Message-ID: <20231012-pranker-usage-09a85a36356f@spud> (raw)
In-Reply-To: <20231012141456.4078-2-jszhang@kernel.org>
[-- Attachment #1: Type: text/plain, Size: 1189 bytes --]
On Thu, Oct 12, 2023 at 10:14:55PM +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>
From v2:
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Thanks,
Conor.
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next prev parent reply other threads:[~2023-10-12 14:37 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-12 14:14 [PATCH v3 0/2] riscv: errata: thead: use riscv_nonstd_cache_ops for CMO Jisheng Zhang
2023-10-12 14:14 ` Jisheng Zhang
2023-10-12 14:14 ` [PATCH v3 1/2] " Jisheng Zhang
2023-10-12 14:14 ` Jisheng Zhang
2023-10-12 14:36 ` Conor Dooley [this message]
2023-10-12 14:36 ` Conor Dooley
2023-10-12 14:14 ` [PATCH v3 2/2] riscv: errata: thead: use pa based instructions " Jisheng Zhang
2023-10-12 14:14 ` Jisheng Zhang
2023-10-12 14:21 ` [PATCH v3 0/2] riscv: errata: thead: use riscv_nonstd_cache_ops " Jisheng Zhang
2023-10-12 14:21 ` Jisheng Zhang
2023-10-12 14:36 ` Conor Dooley
2023-10-12 14:36 ` Conor Dooley
2023-10-12 14:40 ` Jisheng Zhang
2023-10-12 14:40 ` Jisheng Zhang
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