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

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Message-ID: <a159dd5a-7189-308f-9ebc-98f0eadca852@huawei.com>
Date:   Mon, 1 Jun 2020 22:57:35 +0800
From:   Zhenyu Ye <yezhenyu2@...wei.com>
To:     Catalin Marinas <catalin.marinas@....com>
CC:     <linux-arch@...r.kernel.org>, <suzuki.poulose@....com>,
        <maz@...nel.org>, <linux-kernel@...r.kernel.org>,
        <xiexiangyou@...wei.com>, <steven.price@....com>,
        <zhangshaokun@...ilicon.com>, <linux-mm@...ck.org>,
        <arm@...nel.org>, <prime.zeng@...ilicon.com>,
        <guohanjun@...wei.com>, <olof@...om.net>,
        <kuhn.chenqun@...wei.com>, <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: 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/

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