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To: Michael Ellerman , Thomas Gleixner Subject: [PATCH v2 1/2] cpu/SMT: Enable SMT only if a core is online Date: Wed, 31 Jul 2024 08:31:12 +0530 Message-ID: <20240731030126.956210-2-nysal@linux.ibm.com> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240731030126.956210-1-nysal@linux.ibm.com> References: <20240731030126.956210-1-nysal@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-GUID: oyx3NtoUPBi_b8wh_YPYpw34KjCGERzP X-Proofpoint-ORIG-GUID: ZJsosXIEx8nsdNUBJdZ1WvhEEXg1OwB4 X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.28.16 definitions=2024-07-30_21,2024-07-30_01,2024-05-17_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 mlxlogscore=999 priorityscore=1501 adultscore=0 bulkscore=0 mlxscore=0 phishscore=0 spamscore=0 malwarescore=0 suspectscore=0 clxscore=1015 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2407110000 definitions=main-2407310019 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Tyrel Datwyler , Eric DeVolder , Stephen Rothwell , Peter Zijlstra , Nicholas Piggin , linux-kernel@vger.kernel.org, Christophe Leroy , Laurent Dufour , Pawan Gupta , "Nysal Jan K.A" , "Naveen N. Rao" , Sourabh Jain , Michal Suchanek , linuxppc-dev@lists.ozlabs.org, Ard Biesheuvel Errors-To: linuxppc-dev-bounces+incoming=patchwork.ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" From: "Nysal Jan K.A" If a core is offline then enabling SMT should not online CPUs of this core. By enabling SMT, what is intended is either changing the SMT value from "off" to "on" or setting the SMT level (threads per core) from a lower to higher value. On PowerPC the ppc64_cpu utility can be used, among other things, to perform the following functions: ppc64_cpu --cores-on # Get the number of online cores ppc64_cpu --cores-on=X # Put exactly X cores online ppc64_cpu --offline-cores=X[,Y,...] # Put specified cores offline ppc64_cpu --smt={on|off|value} # Enable, disable or change SMT level If the user has decided to offline certain cores, enabling SMT should not online CPUs in those cores. This patch fixes the issue and changes the behaviour as described, by introducing an arch specific function topology_is_core_online(). It is currently implemented only for PowerPC. Fixes: 73c58e7e1412 ("powerpc: Add HOTPLUG_SMT support") Reported-by: Tyrel Datwyler Closes: https://groups.google.com/g/powerpc-utils-devel/c/wrwVzAAnRlI/m/5KJSoqP4BAAJ Signed-off-by: Nysal Jan K.A Reviewed-by: Shrikanth Hegde --- Documentation/ABI/testing/sysfs-devices-system-cpu | 3 ++- kernel/cpu.c | 12 +++++++++++- 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu index 325873385b71..de725ca3be82 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -562,7 +562,8 @@ Description: Control Symmetric Multi Threading (SMT) ================ ========================================= If control status is "forceoff" or "notsupported" writes - are rejected. + are rejected. Note that enabling SMT on PowerPC skips + offline cores. What: /sys/devices/system/cpu/cpuX/power/energy_perf_bias Date: March 2019 diff --git a/kernel/cpu.c b/kernel/cpu.c index 1209ddaec026..b1fd2a3db91a 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -2689,6 +2689,16 @@ int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval) return ret; } +/** + * Check if the core a CPU belongs to is online + */ +#if !defined(topology_is_core_online) +static inline bool topology_is_core_online(unsigned int cpu) +{ + return true; +} +#endif + int cpuhp_smt_enable(void) { int cpu, ret = 0; @@ -2699,7 +2709,7 @@ int cpuhp_smt_enable(void) /* Skip online CPUs and CPUs on offline nodes */ if (cpu_online(cpu) || !node_online(cpu_to_node(cpu))) continue; - if (!cpu_smt_thread_allowed(cpu)) + if (!cpu_smt_thread_allowed(cpu) || !topology_is_core_online(cpu)) continue; ret = _cpu_up(cpu, 0, CPUHP_ONLINE); if (ret)