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Tue, 9 Jun 2026 04:48:28 +0000 (GMT) Message-ID: <11fef529-ca09-422d-a0e5-87eedcb3e900@linux.ibm.com> Date: Tue, 9 Jun 2026 10:18:27 +0530 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 v3 14/20] sched/debug: Provide debugfs to enable/disable steal monitor To: Ilya Leoshkevich , linux-kernel@vger.kernel.org, mingo@kernel.org, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, yury.norov@gmail.com, kprateek.nayak@amd.com Cc: tglx@kernel.org, gregkh@linuxfoundation.org, pbonzini@redhat.com, seanjc@google.com, vschneid@redhat.com, huschle@linux.ibm.com, rostedt@goodmis.org, dietmar.eggemann@arm.com, mgorman@suse.de, bsegall@google.com, maddy@linux.ibm.com, srikar@linux.ibm.com, hdanton@sina.com, chleroy@kernel.org, vineeth@bitbyteword.org, frederic@kernel.org, arighi@nvidia.com, pauld@redhat.com, christian.loehle@arm.com, tj@kernel.org, tommaso.cucinotta@gmail.com, maz@kernel.org, rafael@kernel.org References: <20260514152204.481115-1-sshegde@linux.ibm.com> <20260514152204.481115-15-sshegde@linux.ibm.com> <1bc9ec5b-46d1-4e07-b9a1-82fd7fdee582@linux.ibm.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <1bc9ec5b-46d1-4e07-b9a1-82fd7fdee582@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjA5MDAzOSBTYWx0ZWRfX6nAi7GMdhMJ2 zU6gWkKSwkwCPENDLbhwGiq8FGQwBIst/1o4dFvdpvHAXxsc3LhP7fRyjsteT5pqQixclfOpNHW qZFfk84K18+BpsMOMjNQCUovT7RMfvGa/hvk8na2S7zF0iefk5870O8NMCqypySCegt2fOu9JIZ 8DL3dqJh+dE14LpSsYnAoac5jQICWAvDusOs5pfPmQH3jRovDW8kpe3iuE+uyx4n5hdbU15TNt9 imuVf0pMyIJPRomcXVTP6gm4n5QFJJgZUjBJB3pAvCLOOrQKkeoOKJCdLUt9WDTeraZ73drGbgb +RJHBmka+8YHudoCnBAdlZWZGoI+Kfjq6bN5I/mlY+IVpr5fgE0bMYSVJy8Zt+qaYuFYLwGzgs7 8zdp2cTlfZxqqecfDLfa81GOzW4Dk7qo1bgJwLv3+ETm8XsLvWaxfCxsAv45YL48MaE11shqePZ K7X54DHk0ZA2SW+IQ5g== X-Authority-Analysis: v=2.4 cv=QKhYgALL c=1 sm=1 tr=0 ts=6a279b28 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VnNF1IyMAAAA:8 a=XOy7c0G3JI8abX2cTKQA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: OXIk6WuEHmsHaK2OhAckGxz5vnO4aZgE X-Proofpoint-ORIG-GUID: gTJ4AOI2DpyyywFxdyXa2EFpB2jTTCgX X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-06-09_01,2026-06-09_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 lowpriorityscore=0 bulkscore=0 adultscore=0 phishscore=0 malwarescore=0 impostorscore=0 suspectscore=0 spamscore=0 clxscore=1015 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605210000 definitions=main-2606090039 On 6/8/26 11:07 PM, Ilya Leoshkevich wrote: > > > On 5/14/26 17:21, Shrikanth Hegde wrote: >> Add a debugfs "enable" file to enable steal time monitor. >> >> Computing steal time and acting on it periodically are to be opted by >> the user. This helps to avoid any overhead when the feature >> is disabled. >> >> It is disabled by default. >> >> Signed-off-by: Shrikanth Hegde >> --- >>   kernel/sched/core.c  |  1 + >>   kernel/sched/debug.c | 29 +++++++++++++++++++++++++++++ >>   kernel/sched/sched.h |  2 ++ >>   3 files changed, 32 insertions(+) >> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index 0d1995c65ce6..1533a44d1a6b 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -11270,6 +11270,7 @@ void sched_change_end(struct sched_change_ctx >> *ctx) >>   #ifdef CONFIG_PREFERRED_CPU >>   /* npc - non preferred CPU */ >>   static DEFINE_PER_CPU(struct cpu_stop_work, npc_push_task_work); >> +DEFINE_STATIC_KEY_FALSE(__sched_sm_enable); >>   static int sched_non_preferred_cpu_push_stop(void *arg) >>   { >> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c >> index b1abfdc168bf..be8d223b43fd 100644 >> --- a/kernel/sched/debug.c >> +++ b/kernel/sched/debug.c >> @@ -592,6 +592,33 @@ static void debugfs_ext_server_init(void) >>   #endif /* CONFIG_SCHED_CLASS_EXT */ >>   #ifdef CONFIG_PREFERRED_CPU >> +__read_mostly bool sched_sm_wr_enable; >> + >> +static ssize_t sched_sm_en_write(struct file *filp, const char __user >> *ubuf, >> +                 size_t cnt, loff_t *ppos) >> +{ >> +    bool orig = sched_sm_wr_enable; >> +    ssize_t result; >> + >> +    result = debugfs_write_file_bool(filp, ubuf, cnt, ppos); >> + >> +    if (sched_sm_wr_enable && !orig) { >> +        static_branch_enable(&__sched_sm_enable); >> +    } else if (!sched_sm_wr_enable && orig) { >> +        static_branch_disable(&__sched_sm_enable); >> +        cpumask_copy(&__cpu_preferred_mask, cpu_online_mask); >> +    } > > What if two userspace processes write to this debugfs file concurrently? > I think __sched_sm_enable and __cpu_preferred_mask may go out of sync. > I don't know how realistic is that use-case. But, similar case may be present if CPU hotplug and sched_sm_en_write maybe called in parallel. I can add cpus_read_lock, so that only one can proceed. Does that make sense? This will protect against parallel hotplug too.