From: Will Deacon <will.deacon@arm.com>
To: "huanglingyan (A)" <huanglingyan2@huawei.com>
Cc: Zhangshaokun <zhangshaokun@hisilicon.com>,
linux-arm-kernel@lists.infradead.org, ard.biesheuvel@linaro.org
Subject: Re: [PATCH v3] arm64: lib: accelerate do_csum with NEON instruction
Date: Tue, 8 Jan 2019 13:54:44 +0000
Message-ID: <20190108135444.GB14476@fuggles.cambridge.arm.com> (raw)
In-Reply-To: <9129b882-60f3-8046-0cb9-e0b2452a118d@huawei.com>
[re-adding Ard and LAKML -- not sure why the headers are so munged]
On Mon, Jan 07, 2019 at 10:38:55AM +0800, huanglingyan (A) wrote:
> 在 2019/1/6 16:26, Ard Biesheuvel 写道:
> Please change this into
>
> if (IS_ENABLED(CONFIG_KERNEL_MODE_NEON) &&
> len >= CSUM_NEON_THRESHOLD &&
> may_use_simd()) {
> kernel_neon_begin();
> res = do_csum_neon(buff, len);
> kernel_neon_end();
> }
>
> and drop the intermediate do_csum_arm()
>
>
> + return do_csum_arm(buff, len);
> +#endif /* CONFIG_KERNEL_MODE_NEON */
>
> No else? What happens if len < CSUM_NEON_THRESHOLD ?
>
>
> +#undef do_csum
>
> Can we drop this?
>
> Using NEON instructions will bring some costs. The spending maybe introduced
> when reservering/restoring
> neon registers with kernel_neon_begin()/kernel_neon_end(). Therefore NEON code
> is Only used when
> the length exceeds CSUM_NEON_THRESHOLD. General do csum() codes in lib/
> checksum.c will be used in
> shorter length. To achieve this goal, I use the "#undef do_csum" in else clause
> to have the oppotunity to
> utilize the general codes.
I don't think that's how it works :/
Before we get deeper into the implementation, please could you justify the
need for a CPU-optimised checksum implementation at all? I thought this was
usually offloaded to the NIC?
Will
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Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-06 1:55 Lingyan Huang
2019-01-06 8:26 ` Ard Biesheuvel
[not found] ` <9129b882-60f3-8046-0cb9-e0b2452a118d@huawei.com>
2019-01-08 13:54 ` Will Deacon [this message]
2019-01-09 2:03 ` huanglingyan (A)
2019-01-10 4:08 ` 胡海
2019-01-10 8:14 ` huanglingyan (A)
2019-01-16 16:46 ` Will Deacon
2019-01-18 1:07 ` huanglingyan (A)
2019-01-18 11:14 ` Ard Biesheuvel
2019-02-12 2:26 ` huanglingyan (A)
2019-02-12 7:07 ` Ard Biesheuvel
2019-02-13 8:42 ` huanglingyan (A)
2019-02-13 9:15 ` Ard Biesheuvel
2019-02-13 17:55 ` Ard Biesheuvel
2019-02-14 9:57 ` huanglingyan (A)
2019-02-18 8:49 ` huanglingyan (A)
2019-02-18 9:03 ` Ard Biesheuvel
2019-01-09 14:58 ` Dave Martin
2019-01-10 8:03 ` huanglingyan (A)
2019-01-10 13:53 ` Dave Martin
[not found] <1f065749-6676-6489-14ae-fdcfeeb3389c@huawei.com>
2019-01-07 6:11 ` huanglingyan (A)
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