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Sun, 27 Apr 2025 08:25:39 -0700 (PDT) Date: Sun, 27 Apr 2025 11:25:37 -0400 From: Yury Norov To: Christian Lamparter Cc: linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] wifi: carl9170: micro-optimize carl9170_tx_shift_bm() Message-ID: References: <20250326155200.39895-1-yury.norov@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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 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(): > > > 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 > > Acked-by: Christian Lamparter 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