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Wed, 09 Sep 2026 11:36:32 -0700 (PDT) X-Received: by 2002:a17:90b:1d4f:b0:398:9be5:b417 with SMTP id 98e67ed59e1d1-39b26221eb1mr53821108a91.18.1788978992503; Wed, 09 Sep 2026 11:36:32 -0700 (PDT) Received: from localhost ([50.35.44.179]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1433171a97esm50371041c88.12.2026.09.09.11.36.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Sep 2026 11:36:31 -0700 (PDT) Date: Wed, 9 Sep 2026 11:36:25 -0700 From: Jonathan Cameron To: Oleg Keri Cc: Catalin Marinas , Will Deacon , Mark Rutland , Beata Michalska , Sumit Gupta , Prasanna Kumar T S M , Russell King , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Sudeep Holla , Greg Kroah-Hartman , "Rafael J. Wysocki" , Danilo Krummrich , Viresh Kumar , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, driver-core@lists.linux.dev, linux-pm@vger.kernel.org Subject: Re: [PATCH v1 1/2] arm64: topology: fix arch_freq_get_on_cpu() overflow above 4.19 GHz Message-ID: <20260909113625.000063be@oss.qualcomm.com> In-Reply-To: <08ee55292c1cedf26067d1a2b02fa5657d9650e8.1788712186.git.okerixx@gmail.com> References: <08ee55292c1cedf26067d1a2b02fa5657d9650e8.1788712186.git.okerixx@gmail.com> Organization: Qualcomm X-Mailer: Claws Mail 4.4.0 (GTK 3.24.51; x86_64-w64-mingw32) 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 X-Authority-Analysis: v=2.4 cv=AImJJIpd c=1 sm=1 tr=0 ts=6aa1a731 cx=c_pps a=UNFcQwm+pnOIJct1K4W+Mw==:117 a=aNnz9XPx1a4JIXSYt2cE/A==:17 a=kj9zAlcOel0A:10 a=VdqzKS8jKosA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=yOCtJkima9RkubShWh1s:22 a=pGLkceISAAAA:8 a=vZYCpiARan6kKAuTxo4A:9 a=CjuIK1q_8ugA:10 a=uKXjsCUrEbL0IQVhDsJ9:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTA5MDIwOCBTYWx0ZWRfX0zb4/ZnpPlqZ ib5LkFR0HjXkAGG2MPQMvpmvjxSJFrjuHktucaKRnBouxsttZGA7lw+C4ZnyiCJaUJE/S6tAoI3 yedlu0vYZGilDjdCuQiNRz0LHvbYGhF1J80COsQyLyG7lKTZ3vmKxKbF4kIjNcF3syUzFTbx7Ur SxrkUIkvDvRPcNmIn9lXVcJ+ShgnjYxFZp6wZV+1OxQ/B4Tpr9h22p8gKu3A9UPYRYS6w7BPxTW wsfWMhmC6b1wc24oS74QiHttSlvmrUbC7ZLqLPnZvTyUC1ez0WM2V7QW9DjTDaLvfQWkfsYI5DY /IADQKnc/QruFPtjUgPSxRQgijyIliLTPJqbJlCgVZ1UaRNmbK020VEb+PbUFp5nQO+EHIu4tSU DA8xp6yRAGO02Gp6idjWrd5t9AFzpZyjcz0Xg26aS0lLmYYRxaxlhKvJbeaGC0Sd1F12YA2SLd1 j5O4tdceoNb3fkx3v1g== X-Proofpoint-Spam-Info: AW1haW4tMjYwOTA5MDIwOCBTYWx0ZWRfX7uUQ5KoZukNw vmfTNTgHLtow6RksDbZLy26LEFm+DtA72eEFHdBIPA9uVObMbGJolYc/Cs9ykwLS6cTdhuzEVht UekFbbrYokjz3/r+c0gC72FwkR+N5Zw= X-Proofpoint-ORIG-GUID: DekXrHj_qsvVxJiILyy8nyUoyKgsEVQR X-Proofpoint-GUID: DekXrHj_qsvVxJiILyy8nyUoyKgsEVQR X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-08_03,2026-09-09_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 lowpriorityscore=0 priorityscore=1501 malwarescore=0 impostorscore=0 phishscore=0 adultscore=0 bulkscore=0 suspectscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2609090208 On Sun, 6 Sep 2026 18:37:14 +0200 Oleg Keri wrote: > arch_freq_get_on_cpu() computes the product of the frequency scale and > the reference frequency as a u64, but assigns it to an unsigned int > before shifting it back down: > > freq = scale * arch_scale_freq_ref(cpu); > freq >>= SCHED_CAPACITY_SHIFT; > > The product is truncated to 32 bits before the shift, so the result > wraps once arch_scale_freq_ref() exceeds 2^32 / SCHED_CAPACITY_SCALE, > i.e. 4194304 kHz. > > On a Snapdragon X2 Elite (Glymur) laptop, whose boost OPP is 4723200 > kHz, cpuinfo_avg_freq reports 524283 kHz instead of ~4723200 kHz while > the CPU demonstrably runs at the boost frequency: a fixed workload > completes in 1.72 s at the 4723200 kHz OPP versus 2.01 s at 4032000 > kHz, matching the 1.171 frequency ratio. > > Keep the arithmetic in 64 bits until after the shift. > > Fixes: 16d1e27475f6 ("arm64: Provide an AMU-based version of arch_freq_get_on_cpu") > Signed-off-by: Oleg Keri > --- > arch/arm64/kernel/topology.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > index d28438f8b83f..804758eeb63a 100644 > --- a/arch/arm64/kernel/topology.c > +++ b/arch/arm64/kernel/topology.c > @@ -245,8 +245,9 @@ int arch_freq_get_on_cpu(int cpu) > * (see amu_scale_freq_tick for details) > */ > scale = arch_scale_freq_capacity(cpu); > - freq = scale * arch_scale_freq_ref(cpu); > - freq >>= SCHED_CAPACITY_SHIFT; > + scale *= arch_scale_freq_ref(cpu); > + scale >>= SCHED_CAPACITY_SHIFT; Maybe just do it all one line? freq = (scale * arch_scale_freq_ref(cpu)) >> SCHED_CAPACITY_SHIFT; I was going to suggest that you roll in the arch_scale_freq_capacity() as well but then we'd need a cast to ensure maths was done in 64 bits and that was uglier. I think this should end up the same as what you have. Thanks, Jonathan > + freq = scale; > return freq; > } >