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Wed, 20 Sep 2023 17:47:34 +0000 (GMT) Message-ID: <3f8610b1-ef65-508b-4499-d8d3e34779c6@linux.vnet.ibm.com> Date: Wed, 20 Sep 2023 23:17:32 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [PATCH v3] sched/topology: remove sysctl_sched_energy_aware depending on the architecture Content-Language: en-US To: Valentin Schneider Cc: dietmar.eggemann@arm.com, linux-kernel@vger.kernel.org, ionela.voinescu@arm.com, quentin.perret@arm.com, srikar@linux.vnet.ibm.com, mgorman@techsingularity.net, mingo@kernel.org, pierre.gondois@arm.com, yu.c.chen@intel.com, tim.c.chen@linux.intel.com, mingo@redhat.com, peterz@infradead.org, vincent.guittot@linaro.org References: <20230913114807.665094-1-sshegde@linux.vnet.ibm.com> <7c6dd2ec-b9a9-b364-5a29-05336127e519@linux.vnet.ibm.com> From: Shrikanth Hegde In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: PFDa0bvzFJgVyu9kgK3KDjDAJ9EQsnx2 X-Proofpoint-GUID: 7fD09poa9i7Hxp022KvTcaG7d96wu-Cs X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.980,Hydra:6.0.601,FMLib:17.11.176.26 definitions=2023-09-20_08,2023-09-20_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=999 adultscore=0 clxscore=1015 spamscore=0 priorityscore=1501 impostorscore=0 phishscore=0 suspectscore=0 mlxscore=0 bulkscore=0 malwarescore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2308100000 definitions=main-2309200145 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/15/23 5:30 PM, Valentin Schneider wrote: > On 14/09/23 23:26, Shrikanth Hegde wrote: >> On 9/14/23 9:51 PM, Valentin Schneider wrote: >>> On 13/09/23 17:18, Shrikanth Hegde wrote: >>>> sysctl_sched_energy_aware is available for the admin to disable/enable >>>> energy aware scheduling(EAS). EAS is enabled only if few conditions are >>>> met by the platform. They are, asymmetric CPU capacity, no SMT, >>>> valid cpufreq policy, frequency invariant load tracking. It is possible >>>> platform when booting may not have EAS capability, but can do that after. >>>> For example, changing/registering the cpufreq policy. >>>> >>>> At present, though platform doesn't support EAS, this sysctl is still >>>> present and it ends up calling rebuild of sched domain on write to 1 and >>>> NOP when writing to 0. That is confusing and un-necessary. >>>> >>> >> >> Hi Valentin, Thanks for taking a look at this patch. >> >>> But why would you write to it in the first place? Or do you mean to use >>> this as an indicator for userspace that EAS is supported? >>> >> >> Since this sysctl is present and its value being 1, it gives the >> impression to the user that EAS is supported when it is not. >> So its an attempt to correct that part. >> > > Ah, I see. Then how about just making the sysctl return 0 when EAS isn't > supported? And on top of it, prevent all writes when EAS isn't supported > (perf domains cannot be built, so there would be no point in forcing a > rebuild that will do nothing). > > I can never remember how to properly use the sysctl API, so that's a very > crude implementation, but something like so? > > --- > I tried the below method, instead of sched_energy_enabled, using a helper function which does similar checks as in build_perf_domains and use the same helper function in build_perf_domains as well. # cat sched_energy_aware # echo 0 > sched_energy_aware -bash: echo: write error: Operation not supported # echo 1 > sched_energy_aware -bash: echo: write error: Operation not supported # > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c > index 05a5bc678c089..dadfc5afc4121 100644 > --- a/kernel/sched/topology.c > +++ b/kernel/sched/topology.c > @@ -230,9 +230,28 @@ static int sched_energy_aware_handler(struct ctl_table *table, int write, > if (write && !capable(CAP_SYS_ADMIN)) > return -EPERM; > > + if (!sched_energy_enabled()) { > + if (write) > + return -EOPNOTSUPP; > + else { > + size_t len; > + > + if (*ppos) { > + *lenp = 0; > + return 0; Is it possible for *ppos to be 0? if so in which scenario? and Does it make sense to make length as 0 unconditionally if eas is not possible? > + } > + > + len = snprintf((char *)buffer, 3, "0\n"); > + > + *lenp = len; > + *ppos += len; > + return 0; > + } > +> ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);