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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, Sibi Sankar Subject: Re: [PATCH v2 1/2] arm64: topology: fix arch_freq_get_on_cpu() overflow above 4.19 GHz Message-ID: <20260909152014.000055d8@oss.qualcomm.com> In-Reply-To: <20260909192351.33910-2-okerixx@gmail.com> References: <20260909192351.33910-1-okerixx@gmail.com> <20260909192351.33910-2-okerixx@gmail.com> Organization: Qualcomm X-Mailer: Claws Mail 4.4.0 (GTK 3.24.51; x86_64-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Proofpoint-Spam-Info: AW1haW4tMjYwOTA5MDI1MSBTYWx0ZWRfX74WcbSBtgMq4 iVm1B1AvWHhvQnrUJ7k6m5We9n6DWkois5gj1HZAhHoQtAjrc7i+Yqc0xfoT0NTv31UYkAn+sTT CswO4mjg7k5ywahfDIJ9c9zn2JGzuT8= X-Proofpoint-ORIG-GUID: 38lL9HubXEYL91JPCT9UAwXlPAg2gENR X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTA5MDI1MSBTYWx0ZWRfXwrxh6qjP5h1Z XcBp/+cw5m1QM/7ew3Q1mK+iZCsI90kgZOOQgJlqlWmT9bg6C9e5ernm58Le+XcWr5wWyTWZf3v cVdvnSvWPXpU8oB5PMoKG2YyHOQaWNLwkzLxAVXL9WwINpJIXiLq2iRgGE1cs/0YN/hjLCVYCSW rcOEk6jRawQSgSHX96uLwWeoKYW8GCsxi7/T2ooTKB/7Rf7/jAWh/dp/ZueVTwSPoAvtPlkj2rm F+VSodpBxiZBeSB+shUNJ8QLdIIVxPZeuULE5UWh4BXvYWgP5xrSzTaI3Yh8ENjzwVHoOtz/8Qo EpLB+vcVQamzhICiza+WbkTIP/LZuSx3hh+MkQ4NxpcoTmiGjWpKrv0h2pe3d29KUH4UgtvIHs8 3sYikg8bdwr38hc+tp14BF/UducvCrsS79cH346B7UaHkQTq2pSAqll9hPHXun2V+DAFNtK1/s2 RAK1AgtLtrmB24eIafQ== X-Authority-Analysis: v=2.4 cv=H5pOUOYi c=1 sm=1 tr=0 ts=6aa1dba4 cx=c_pps a=vVfyC5vLCtgYJKYeQD43oA==:117 a=aNnz9XPx1a4JIXSYt2cE/A==:17 a=kj9zAlcOel0A:10 a=VdqzKS8jKosA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=yx91gb_oNiZeI1HMLzn7:22 a=pGLkceISAAAA:8 a=EUspDBNiAAAA:8 a=GPoSAeC3DJVMy4bTL1oA:9 a=CjuIK1q_8ugA:10 a=rl5im9kqc5Lf4LNbBjHf:22 X-Proofpoint-GUID: 38lL9HubXEYL91JPCT9UAwXlPAg2gENR 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=2026-09-09_02,2026-09-09_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 suspectscore=0 spamscore=0 priorityscore=1501 impostorscore=0 malwarescore=0 bulkscore=0 adultscore=0 lowpriorityscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609090251 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260909_152021_981514_62E84DD4 X-CRM114-Status: GOOD ( 24.64 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, 9 Sep 2026 21:23:50 +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") > Suggested-by: Jonathan Cameron You don't add that for a review comment unless it results in a whole new patch. +CC Sibi who is a whole lot more familiar with Glymur than I am! Jonathan > Signed-off-by: Oleg Keri > --- > arch/arm64/kernel/topology.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > index d28438f8b83f..0eca321ff113 100644 > --- a/arch/arm64/kernel/topology.c > +++ b/arch/arm64/kernel/topology.c > @@ -245,8 +245,7 @@ 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; > + freq = (scale * arch_scale_freq_ref(cpu)) >> SCHED_CAPACITY_SHIFT; > return freq; > } >