linux-kernel - Re: [PATCH V3 2/2] riscv: Use use_asid

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Date:   Tue, 25 May 2021 14:35:56 +0200
From:   Christoph Hellwig <hch@....de>
To:     guoren@...nel.org
Cc:     anup.patel@....com, palmerdabbelt@...gle.com, arnd@...db.de,
        hch@....de, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-sunxi@...ts.linux.dev, Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH V3 2/2] riscv: Use use_asid_allocator flush TLB

On Tue, May 25, 2021 at 12:24:07PM +0000, guoren@...nel.org wrote:
> From: Guo Ren <guoren@...ux.alibaba.com>
> 
> Use static_branch_unlikely(&use_asid_allocator) to keep the origin
> tlb flush style, so it's no effect on the existing machine. Here
> are the optimized functions:
>  - flush_tlb_mm
>  - flush_tlb_page
>  - flush_tlb_range
> 
> All above are based on the below new implement functions:
>  - __sbi_tlb_flush_range_asid
>  - local_flush_tlb_range_asid


This mentiones what functions you're changing, but not what the
substantial change is, and more importantly why you change it.

> +static inline void local_flush_tlb_range_asid(unsigned long start, unsigned long size,
> +					      unsigned long asid)

Crazy long line.  Should be:

static inline void local_flush_tlb_range_asid(unsigned long start,
		unsigned long size, unsigned long asid)

> +{
> +	unsigned long tmp = start & PAGE_MASK;
> +	unsigned long end = ALIGN(start + size, PAGE_SIZE);
> +
> +	if (size == -1) {
> +		__asm__ __volatile__ ("sfence.vma x0, %0" : : "r" (asid) : "memory");
> +		return;

Please split the global (size == -1) case into separate helpers.

> +	while(tmp < end) {

Missing whitespace befre the (.

Also I think this would read nicer as:

	for (tmp = start & PAGE_MASK; tmp < end; tmp += PAGE_SIZE)

> +static void __sbi_tlb_flush_range_asid(struct cpumask *cmask, unsigned long start,
> +				       unsigned long size, unsigned long asid)

Another overly long line.

Also for all thee __sbi_* functions, why the __ prefix?

> +	if (cpumask_any_but(cmask, cpuid) >= nr_cpu_ids) {
> +		local_flush_tlb_range_asid(start, size, asid);
> +	} else {
> +		riscv_cpuid_to_hartid_mask(cmask, &hmask);
> +		sbi_remote_sfence_vma_asid(cpumask_bits(&hmask), start, size, asid);

Another long line (and a few more later).