Re: [RFC PATCH v3 2/2] arm64: tlb: Use the TLBI RANGE feature in arm64

Hi Catalin,

I have sent the v4 of this series [1] and combine the two function with
a single loop.  See codes for details.

[1] https://lore.kernel.org/linux-arm-kernel/20200601144713.2222-1-yezhenyu2@huawei.com/ (local)

On 2020/5/21 1:08, Catalin Marinas wrote:

quoted

This optimization is only effective when the range is a multiple of 256KB
(when the page size is 4KB), and I'm worried about the performance
of ilog2().  I traced the __flush_tlb_range() last year and found that in
most cases the range is less than 256K (see details in [1]).

THP or hugetlbfs would exercise bigger strides but I guess it depends on
the use-case. ilog2() should be reduced to a few instructions on arm64
AFAICT (haven't tried but it should use the CLZ instruction).

Not bigger than 256K, but the range must be a integer multiple of 256KB,
so I still start from scale 0.

Thanks,
Zhenyu


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