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Mon, 12 Oct 2026 12:14:59 +0000 (GMT) Received: from linux.ibm.com (unknown [9.126.150.29]) by smtpav05.fra02v.mail.ibm.com (Postfix) with SMTP; Mon, 12 Oct 2026 12:14:59 +0000 (GMT) Date: Mon, 12 Oct 2026 17:44:58 +0530 From: Srikar Dronamraju To: Shrikanth Hegde Cc: maddy@linux.ibm.com, linuxppc-dev@lists.ozlabs.org, peterz@infradead.org, tim.c.chen@linux.intel.com, christophe.leroy@csgroup.eu, linux-kernel@vger.kernel.org, ritesh.list@gmail.com, kprateek.nayak@amd.com, yu.c.chen@intel.com, vineethr@linux.ibm.com, vincent.guittot@linaro.org, npiggin@gmail.com, mpe@ellerman.id.au Subject: Re: [PATCH 1/4] powerpc/topology: Introduce llc_override debug knob Message-ID: Reply-To: Srikar Dronamraju References: <20261012102037.2477378-1-sshegde@linux.ibm.com> <20261012102037.2477378-2-sshegde@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20261012102037.2477378-2-sshegde@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDEyMDA0OCBTYWx0ZWRfX6y9g+98Y80zg Hf9VnGx8KKCqtOSpyYwe+V+7FyD7xOWY6ySZay8duffa8ELZBoavmrOb9+iW7Zg9DJnfxNpjtri q4wAfGbR17055+KHuZKKS7n3mTuYby55LAmkK4AVwGj8DGJ5rtGg6WqF2X7J0sOC505LAXP9cc8 s8EXh6SHY8euWdK9K7FCKvchk7Rz9yvDJQTePFdhlI/oyfllqeAH36p5+82xR5u/djp7XWDlAQo g2zUA8WSNmJ9uh82UYzMdm1BllRh6ElvS7n1NIAFgeEptd0EFwFlcpj12W6SDwQFtukmMKJilWP tDvCuctaOJ2V51TqnF3LsplOKxIf1069kxBacmZKZE2Cwp+ooRPAYplLYHHCFABRGky06HbOxaW UeoSwQcvaUrvKrk9yq9LLnLGRYA9kZq5cnwtZMDmlFhD6yiin/IGMnq8D1VEPidhFdrnOhHpmTL te/qTN8weyu26IDIyYA== X-Proofpoint-GUID: 2cuUwQ5KEcxni8N6IxmeU7JYiff81cT0 X-Proofpoint-ORIG-GUID: cRyUIli8e6wfR9VL_M0INNbuS5_TP662 X-Proofpoint-Spam-Info: AW1haW4tMjYxMDEyMDA0OCBTYWx0ZWRfXxOgiZLG5IZel eFZ72b5J5iQOuWNCvGWf91dPKlNA9ebEmFfqY1Wq4hYaOr98fvmASEKImivRpBGMKzIuTr6shfQ Q0d3BugErC18yAzdA1JA2VULF6agZZY= X-Authority-Analysis: v=2.4 cv=btHZl0ai c=1 sm=1 tr=0 ts=6acccf4b cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=8nJEP1OIZ-IA:10 a=660iZSQnnn4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VnNF1IyMAAAA:8 a=hudXqxXAy8cwXFPxgu4A:9 a=wPNLvfGTeEIA:10 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=2026-10-12_04,2026-10-09_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 malwarescore=0 phishscore=0 impostorscore=0 adultscore=0 lowpriorityscore=0 priorityscore=1501 clxscore=1011 spamscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610080000 definitions=main-2610120048 * Shrikanth Hegde [2026-10-12 15:50:34]: Hi Shrikanth, > > As a result, it may be enabled but has no room to operate. > Hence provide a debugfs option one can set to try experiment their > workload with cache aware scheduling. This also provides ways to explore > it on system with SMT=4 to see if there are any opportunities > to improve or uncover bugs if there is any. > > This does not change the hardware cache topology. It only changes the > sched-domain level at which SD_SHARE_LLC is set. > > Initially start with, > - New debugs file called llc_override. It can be set/get on > /sys/kernel/debug/powerpc/llc_override > - Adds parser logic for the debug knob. > This is a good way to allow experimenting to know if a software override of the LLC esp given the latency numbers within hemisphere and chip. > There is no point in setting NUMA as the LLC domain. So give option > until pkg to experiment with. > > Actual flag manipulations and rebuilding sched domains are introduced > in subsequent patches. > > Signed-off-by: Shrikanth Hegde > --- > PS: Split is deliberate. If squashing all this into one patch helps, > let me know. > > arch/powerpc/kernel/smp.c | 90 +++++++++++++++++++++++++++++++++++++++ > 1 file changed, 90 insertions(+) > > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c > index 6a5a5469aaae..433757511adb 100644 > --- a/arch/powerpc/kernel/smp.c > +++ b/arch/powerpc/kernel/smp.c > @@ -36,6 +36,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -1826,3 +1827,92 @@ void __noreturn arch_cpu_idle_dead(void) > } > > #endif > + > +enum llc_override_values { > + LLC_OVERRIDE_DISABLED, > + LLC_OVERRIDE_SMT, > + LLC_OVERRIDE_MC, > + LLC_OVERRIDE_PKG, > +}; > + For the current experiments, would it help to keep it simple and have just SMT and MC. I mean we can include disabled and pkg based on our experiments. -- Thanks and Regards Srikar Dronamraju