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Subject: Re: [PATCH] riscv: enable GENERIC_FIND_FIRST_BIT
To:     Jisheng Zhang <jszhang3@mail.ustc.edu.cn>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>
CC:     <linux-riscv@lists.infradead.org>, <linux-kernel@vger.kernel.org>
References: <20210718001423.6b8e1d23@xhacker>
 <20210908230427.3a92fb87@xhacker>
From:   Kefeng Wang <wangkefeng.wang@huawei.com>
Message-ID: <bbd220c4-b535-d024-6bd3-b620b4702ed3@huawei.com>
Date:   Thu, 9 Sep 2021 08:58:31 +0800
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On 2021/9/8 23:04, Jisheng Zhang wrote:
> Hi Palmer,
>
> On Sun, 18 Jul 2021 00:14:23 +0800
> Jisheng Zhang wrote:
>
>> From: Jisheng Zhang <jszhang@kernel.org>
>>
>> riscv doesn't implement architecture-optimized bitsearching functions
>> such as find_first_{zero}_bit() etc.
>>
>> When GENERIC_FIND_FIRST_BIT=n, find_first_bit() is implemented with
>> find_next_bit() which is less efficient. Enable GENERIC_FIND_FIRST_BIT
>> for riscv to get more optimized find_first_bit() implementation, an
>> initial test(lib/find_bit_benchmark) shows find_first_bit() performance
>> is improved by nearly 32%.
> It seems this patch is missed. Is it possible to pick it up for 2nd 5.15-rc1 PR?
>
> Thanks

It is enabled unconditionally by following commit

commit dbbccfe505ef8fae804677abf0564c1e07479102

Author: Yury Norov <yury.norov@gmail.com>
Date:   Tue Aug 24 09:59:56 2021 +1000

     arch: remove GENERIC_FIND_FIRST_BIT entirely

>
>> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
>> ---
>>   arch/riscv/Kconfig | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index 8fcceb8eda07..7ebc54c5c245 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -47,6 +47,7 @@ config RISCV
>>   	select GENERIC_ATOMIC64 if !64BIT
>>   	select GENERIC_CLOCKEVENTS_BROADCAST if SMP
>>   	select GENERIC_EARLY_IOREMAP
>> +	select GENERIC_FIND_FIRST_BIT
>>   	select GENERIC_GETTIMEOFDAY if HAVE_GENERIC_VDSO
>>   	select GENERIC_IOREMAP
>>   	select GENERIC_IRQ_MULTI_HANDLER
>
>
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>