From:   David Laight <David.Laight@ACULAB.COM>
To:     'Huacai Chen' <chenhuacai@loongson.cn>,
        Arnd Bergmann <arnd@arndb.de>,
        Huacai Chen <chenhuacai@kernel.org>
CC:     "loongarch@lists.linux.dev" <loongarch@lists.linux.dev>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        Xuefeng Li <lixuefeng@loongson.cn>,
        Guo Ren <guoren@kernel.org>, Xuerui Wang <kernel@xen0n.name>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "loongson-kernel@lists.loongnix.cn" 
        <loongson-kernel@lists.loongnix.cn>
Subject: RE: [PATCH V3] LoongArch: Provide kernel fpu functions
Thread-Topic: [PATCH V3] LoongArch: Provide kernel fpu functions
Thread-Index: AQHZUBJ45VTcAaETSEKOkFhUUQ2cwq7t95nA
Date:   Mon, 6 Mar 2023 16:57:57 +0000
Message-ID: <5171500c01604a70b55529d8cd780a57@AcuMS.aculab.com>
References: <20230306095934.609589-1-chenhuacai@loongson.cn>
In-Reply-To: <20230306095934.609589-1-chenhuacai@loongson.cn>
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From: Huacai Chen
> Sent: 06 March 2023 10:00
> 
> Provide kernel_fpu_begin()/kernel_fpu_end() to allow the kernel itself
> to use fpu. They can be used by some other kernel components, e.g., the
> AMDGPU graphic driver for DCN.
> 
...
> +void kernel_fpu_end(void)
> +{
> +	if (!this_cpu_read(in_kernel_fpu))
> +		return;

Shouldn't it be better for that to be a counter?
Not sure what anyone else does.

> +
> +	if (!is_fpu_owner())
> +		disable_fpu();
> +	else
> +		_restore_fp(&current->thread.fpu);

Does that actual do the restore?
You really don't need to do it until 'return to user'.
That will speed up a subsequent kernel_fpu_begin().

If fact, couldn't kernel_fpu_end() just be preemt_enable()?

	David

> +
> +	this_cpu_write(in_kernel_fpu, false);
> +	preempt_enable();
> +}
> +EXPORT_SYMBOL(kernel_fpu_end);
> --
> 2.39.1

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