linux-kernel - Re: [PATCH] wifi: carl9170: micro-optimize carl9170_tx_shift

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Message-ID: <54f50afa-3267-4829-8be6-1542c3fef606@oss.qualcomm.com>
Date: Tue, 20 May 2025 09:24:14 -0700
From: Jeff Johnson <jeff.johnson@....qualcomm.com>
To: Yury Norov <yury.norov@...il.com>,
        Christian Lamparter <chunkeey@...il.com>
Cc: linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] wifi: carl9170: micro-optimize carl9170_tx_shift_bm()

On 4/27/2025 8:25 AM, Yury Norov wrote:
> On Wed, Mar 26, 2025 at 09:00:33PM +0100, Christian Lamparter wrote:
>> Hi,
>>
>> On Wed, Mar 26, 2025 at 4:52 PM Yury Norov <yury.norov@...il.com> wrote:
>>>
>>> The function calls bitmap_empty() just before find_first_bit(). Both
>>> functions are O(N). Because find_first_bit() returns >= nbits in case of
>>> empty bitmap, the bitmap_empty() test may be avoided.
>>>
>>
>> I looked up bitmap_empty():
>> <https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/bitmap.h#n423>
>>
>> apart from the small_const_nbits stuff (which carl9170 likely does not qualify
>> for since from what I remember it's a 128bits bitmap) the function just does:
>>
>> |   return find_first_bit(src, nbits) == nbits;
>>
>> so yes, find_first_bit runs twice with same parameters... Unless the
>> compiler is smart
>> enough to detect this and (re-)use the intermediate result later. But
>> I haven't check
>> if this is the case with any current, old or future compilers. Has anyone?
>>
>> Anyway, Sure.
>>
>>> Signed-off-by: Yury Norov <yury.norov@...il.com>
>>
>> Acked-by: Christian Lamparter <chunkeey@...il.com>
> 
> Thanks, Chrustian. So, how is that supposed to be merged?
> I can move it with bitmap-for-next, unless there's no better
> branch.
> 
> Thanks,
> Yury
> 

Yury, did you take this?
If not, I'll take it through the ath tree.