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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-432bd0dad8bsm28021253f8f.8.2026.01.10.03.54.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 10 Jan 2026 03:54:44 -0800 (PST) Date: Sat, 10 Jan 2026 11:54:39 +0000 From: David Laight To: "Maciej W. Rozycki" Cc: Yury Norov , Petr Tesarik , Yury Norov , Rasmus Villemoes , Richard Henderson , Matt Turner , Magnus Lindholm , Vineet Gupta , Geert Uytterhoeven , Thomas Bogendoerfer , Madhavan Srinivasan , Michael Ellerman , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Chris Zankel , Max Filippov , Patrik Jakobsson , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Robin Murphy , Joerg Roedel , Will Deacon , Jakub Kicinski , Andrew Lunn , "David S. Miller" , Eric Dumazet , Paolo Abeni , Oliver Neukum , Arnd Bergmann , Kuan-Wei Chiu , Andrew Morton , Marcel Holtmann , Johan Hedberg , Luiz Augusto von Dentz , Pablo Neira Ayuso , Florian Westphal , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 2/2] treewide, bits: use ffs_val() where it is open-coded Message-ID: <20260110115439.184b7a66@pumpkin> In-Reply-To: References: <1ce341045ad0487c66ca21003f9974916aba0bce.1767975412.git.ptesarik@suse.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) 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=US-ASCII Content-Transfer-Encoding: 7bit On Sat, 10 Jan 2026 10:36:07 +0000 (GMT) "Maciej W. Rozycki" wrote: > On Fri, 9 Jan 2026, Yury Norov wrote: > > > > diff --git a/arch/alpha/kernel/smp.c b/arch/alpha/kernel/smp.c > > > index ed06367ece574..2f3809c015b99 100644 > > > --- a/arch/alpha/kernel/smp.c > > > +++ b/arch/alpha/kernel/smp.c > > > @@ -525,7 +525,7 @@ handle_ipi(struct pt_regs *regs) > > > do { > > > unsigned long which; > > > > > > - which = ops & -ops; > > > + which = ffs_val(ops); > > > ops &= ~which; > > > which = __ffs(which); > > > > I guess, this should be: > > > > which = __ffs(ops); > > ops &= ops - 1; > > I think it's the wrong operation order. If you are going to do the __ffs() do it first. which = __ffs(ops); ops &= ~(1u << which); OTOH what follows is: switch (which) { case IPI_RESCHEDULE: so changing to 'case 1u << IPI_RESCHEDULE: would save the ffs(). But the entire loop is pointless, three tests, the first being: if (op & (1u << IPI_RESCHEDULE)) scheduler_ipi(); would be far less code. But probably pointless churn - no one cares about alpha any more :-) > > > > diff --git a/arch/mips/dec/ecc-berr.c b/arch/mips/dec/ecc-berr.c > > > index 1eb356fdd8323..8934b8b1cf375 100644 > > > --- a/arch/mips/dec/ecc-berr.c > > > +++ b/arch/mips/dec/ecc-berr.c > > > @@ -153,7 +153,7 @@ static int dec_ecc_be_backend(struct pt_regs *regs, int is_fixup, int invoker) > > > /* Ack now, now we've rewritten (or not). */ > > > dec_ecc_be_ack(); > > > > > > - if (syn && syn == (syn & -syn)) { > > > + if (syn && syn == ffs_val(syn)) { > > > > It opencodes is_power_of_2(). Badly... David > > Correct and it also predates that helper's existence by ~4 years. I'll > be happy to see this converted as the intent will be obviously clearer. > > Maciej >