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

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Message-ID: <aCyupkU1tK-bUlZV@yury>
Date: Tue, 20 May 2025 12:32:38 -0400
From: Yury Norov <yury.norov@...il.com>
To: Jeff Johnson <jeff.johnson@....qualcomm.com>
Cc: Christian Lamparter <chunkeey@...il.com>,
	linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] wifi: carl9170: micro-optimize carl9170_tx_shift_bm()

On Tue, May 20, 2025 at 09:24:14AM -0700, Jeff Johnson wrote:
> 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.

No. Please take with ath.