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Tue, 15 Apr 2025 09:58:02 +0800 X-QQ-mid: xmsmtpt1744682282t8jvjypwn Message-ID: X-QQ-XMAILINFO: NnA3IMNPwBd++tNcGlwsbS2vzUr7sFx8qwGAEaazHKzVw3QDoVB8JgKDimnkbP FO1pT1gL9hr+XL8Xf0Kww4CxbHcoyc6t8dKYndsSEUU4yfek18jqpLtH8BbwfRMYbG3/izivvmTW +BzUDQIdnXs98dAwOA2bCQsSVz3bKFubvNu9XRMgN/2WvANE4FGKEYEOuDlC5dW0aSUpJs3yoSXd +usZEYe3+uwMsJmN7N0HLwEL1UVgq7zJNv47ME7gvQhjYX55wqepYSKi0q+z/zK+rkS9D5GhNuyh RskbJYpx0lH0L+eB1xWULXk9uCyubDBACGMs56uTCLUvGDmmUuf0D6Q26wq6nKDGOkttksbkcV6n AVC30rV0hEys+G9twzGm7a2L7pk7rjfQIULyeQeK3sn1N0xLEI5lk+sIhY/xIygGdF0H7kH0J1jT T5fMzjlD9zfeGIx/mN89tJD4fSeBUeJTXbFG3b+CfKMc/8QfF5TZSU7/ddZU769pnaw/pNAWgHNL 6gBGF1bt0Pm8mJiDWapU+GezON4+zCB7HnyqRj7OtE4A3JKqqfa2NcbVpYQ6uBTLie2ccXN6KuhS xeZ1bRAt5S+/172IociRZqgFMIXYmV91Ly/IpYAytAY52kuZdSsZnOL9p7yLhytGbPoq+r1LH/JG NQsAKXOBdvQiTzFMa+lm7OkTDqhAJ/P6P5ZNES1LhqOY/9JsfiZHlA+PxjG+zmW0Eyer3VcJAH3r 3oldLQqKLttVBC0i+k9knL/3MnNt+ys5qIDXIwBi/IQznC8/+72hAwwoG825UtyNV1AzF44w+gtG vY4fl5Y+Bf8Z6dT5ZObmkQItaHi6WjM2uUf9SMaGvppnH58UM+VFy+uUAj/z6WLFOhkNO8ATqb/S M/R/vZqXppYJI+PSU7WlPuyBsR19TrlzL7M0BpHjBhg+ipA86TdV3eXlaUUqCU2FMGniKnstOeFo CqPp/MnRKi0Bl5EAnkedsZ95fPylEIKrMP6P8edbgCI3gjrqVME3ZVtomCnBb/ewUupDNCIOM= X-QQ-XMRINFO: MPJ6Tf5t3I/ycC2BItcBVIA= X-OQ-MSGID: <5a20548a-ac36-4c4c-ab18-f8936719e5cf@qq.com> Date: Tue, 15 Apr 2025 09:58:01 +0800 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 v2] PM: EM: Fix potential division-by-zero error in em_compute_costs() From: Yaxiong Tian To: Lukasz Luba Cc: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, Yaxiong Tian , rafael@kernel.org References: <143378b0-5740-4f2b-9a79-f04cf9ef1f77@arm.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2025/4/15 09:12, Yaxiong Tian 写道: > > > 在 2025/4/14 16:08, Lukasz Luba 写道: >> Hi Yaxiong, >> >> On 4/11/25 02:28, Yaxiong Tian wrote: >>> From: Yaxiong Tian >>> >>> When the device is of a non-CPU type, table[i].performance won't be >>> initialized in the previous em_init_performance(), resulting in division >>> by zero when calculating costs in em_compute_costs(). >>> >>> Since the 'cost' algorithm is only used for EAS energy efficiency >>> calculations and is currently not utilized by other device drivers, we >>> should add the _is_cpu_device(dev) check to prevent this >>> division-by-zero >>> issue. >>> >>> Fixes: <1b600da51073> ("PM: EM: Optimize em_cpu_energy() and remove >>> division") >>> Signed-off-by: Yaxiong Tian >>> --- >>>   kernel/power/energy_model.c | 2 +- >>>   1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c >>> index d9b7e2b38c7a..d1fa7e8787b5 100644 >>> --- a/kernel/power/energy_model.c >>> +++ b/kernel/power/energy_model.c >>> @@ -244,7 +244,7 @@ static int em_compute_costs(struct device *dev, >>> struct em_perf_state *table, >>>                       cost, ret); >>>                   return -EINVAL; >>>               } >>> -        } else { >>> +        } else if (_is_cpu_device(dev)) { >>>               /* increase resolution of 'cost' precision */ >>>               power_res = table[i].power * 10; >>>               cost = power_res / table[i].performance; >> >> >> As the test robot pointed out, please set the 'cost' to 0 >> where it's declared. >> >> The rest should be fine. >> >> Regards, >> Lukasz > > Sorry, the V3 version with cost=0 still has issues. > > I noticed that if the cost is set to 0, the condition "if (table[i].cost >  >= prev_cost)" in the following code will always evaluate to true. This >  will incorrectly set the flags to EM_PERF_STATE_INEFFICIENT. > > Should we change ">=" to ">"? > Sorry Again， Setting EM_PERF_STATE_INEFFICIENT in this case is correct. Earlier, I misunderstood the definition/usage of EM_PERF_STATE_INEFFICIENT.