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Wed, 15 Apr 2026 11:14:06 -0700 (PDT) Received: from [192.168.1.100] ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-488f09611ecsm26538875e9.9.2026.04.15.11.14.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 15 Apr 2026 11:14:05 -0700 (PDT) Message-ID: <27651a34-6b25-430f-8cb4-39d44b2d4c90@gmail.com> Date: Wed, 15 Apr 2026 20:14:04 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] sched/rt: Use atomic_try_cmpxchg_acquire() in rto_start_trylock() To: David Carlier , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak Cc: linux-kernel@vger.kernel.org References: <20260415124045.372307-1-devnexen@gmail.com> Content-Language: en-US From: Uros Bizjak In-Reply-To: <20260415124045.372307-1-devnexen@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 4/15/26 14:40, David Carlier wrote: > Replace this pattern in rto_start_trylock(): > > !atomic_cmpxchg_acquire(*ptr, 0, new) > > ... with the simpler and faster: > > atomic_try_cmpxchg_acquire(*ptr, &zero, new) > > The x86 CMPXCHG instruction returns success in the ZF flag, so > atomic_try_cmpxchg_acquire() saves a compare after the CMPXCHG. > > No functional change intended. > > Signed-off-by: David Carlier Reviewed-by: Uros Bizjak > --- > kernel/sched/rt.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index 4ee8faf01441..13ac94899c18 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -2172,7 +2172,8 @@ static int rto_next_cpu(struct root_domain *rd) > > static inline bool rto_start_trylock(atomic_t *v) > { > - return !atomic_cmpxchg_acquire(v, 0, 1); > + int zero = 0; > + return atomic_try_cmpxchg_acquire(v, &zero, 1); > } > > static inline void rto_start_unlock(atomic_t *v)