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Mon, 6 Jul 2026 08:47:16 +0000 (GMT) Message-ID: <8efa7a72-18c1-44b8-aaaf-80006a7c8fff@linux.ibm.com> Date: Mon, 6 Jul 2026 14:17:15 +0530 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 17/23] virt/steal_monitor: Provide default method to get systemwide steal time To: Yury Norov Cc: 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, iii@linux.ibm.com, corbet@lwn.net, 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, 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, rdunlap@infradead.org, kernellwp@gmail.com, linux-doc@vger.kernel.org References: <20260701141654.500125-1-sshegde@linux.ibm.com> <20260701141654.500125-18-sshegde@linux.ibm.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=KsJ9H2WN c=1 sm=1 tr=0 ts=6a4b6ba3 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VnNF1IyMAAAA:8 a=y1RYhKU3uvHFaDme0DIA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzA2MDA4MyBTYWx0ZWRfX3TJAyHYtCgRz 13v+d4FRGbY+YvndknJWQ8rBdXa9Gc+ro73Av4oywl9z4SJSoaF/w6syTDCeqeMkKgt7sKmpcvQ 5p2BKX86JjKWTQ1lfuefifwSUJeZ5J4= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzA2MDA4MyBTYWx0ZWRfX3gnjdW26G43h sWRax4W9fbAcnbnwUkWaMZgPiZLp1FntA7YHLbETuAcEmA50jfZQ+/Gbje9fRqBArBHYzDyNrH2 oDJ5tHQ9lL1fZNWZ+fQ+L1pr5KEGUOEmK7zHuhrkA3PfD083k80rOmi73exdC1CdAPLuy4f0WCE ljvbwvpT4UcXxlTx0zZ/fPa8EUG28sDzjbKP2YvB0pQWpow2aycDIpyq0ADL3yPZyxk1Cj0gLrq Nr2TRKPfiNMWonL7KRoOVfIi4+yR3mR2kQLX3aXd3uSKT5vpi2sSiL8OEmxokKY4LEu8ZVb9w0J sHsVReXqKu6H+xXbK5nk19dUcWWyT6gNGEg5OBj0KcxB5YfBEU5pSMLRFYLnfG9QRL4rL5yc+vH t4bMkxLe1feq2QMWD/98ewZBzFlj5yoPIpamVaTk3Wqf3T5AzmEvp6g2oALf6blN6V6CIFpB8ml lqOXL5ir0i55wsGq2AQ== X-Proofpoint-ORIG-GUID: ej5gsWGFbsm7-AY4bTQWvRbZmmJ9CyIE X-Proofpoint-GUID: 42FPwaWLWfX3u8QtVjjPdTG4kyB5wcyO 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=2026-07-05_02,2026-07-03_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 malwarescore=0 spamscore=0 adultscore=0 clxscore=1015 suspectscore=0 lowpriorityscore=0 priorityscore=1501 bulkscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607060083 On 7/4/26 12:46 AM, Yury Norov wrote: > On Wed, Jul 01, 2026 at 07:46:48PM +0530, Shrikanth Hegde wrote: >> steal monitor takes global view of steal time instead of individual >> vCPU. For this collect overall steal values across all the vCPUs or >> vCPUs of interest. >> >> Default implementation chooses steal time across all active CPUs. >> >> Signed-off-by: Shrikanth Hegde >> --- >> v5->v6: >> - Add cpus_read_lock() for hotplug safety >> >> drivers/virt/steal_monitor/Makefile | 2 +- >> drivers/virt/steal_monitor/defaults.c | 28 +++++++++++++++++++++++++++ >> drivers/virt/steal_monitor/sm_core.h | 3 +++ >> 3 files changed, 32 insertions(+), 1 deletion(-) >> create mode 100644 drivers/virt/steal_monitor/defaults.c >> >> diff --git a/drivers/virt/steal_monitor/Makefile b/drivers/virt/steal_monitor/Makefile >> index 24cee55342ce..7c16f8cf9583 100644 >> --- a/drivers/virt/steal_monitor/Makefile >> +++ b/drivers/virt/steal_monitor/Makefile >> @@ -11,4 +11,4 @@ >> # >> obj-$(subst y,m,$(CONFIG_PREFERRED_CPU)) += steal_monitor.o >> >> -steal_monitor-y := sm_core.o >> +steal_monitor-y := sm_core.o defaults.o >> diff --git a/drivers/virt/steal_monitor/defaults.c b/drivers/virt/steal_monitor/defaults.c >> new file mode 100644 >> index 000000000000..6681f9938f6a >> --- /dev/null >> +++ b/drivers/virt/steal_monitor/defaults.c >> @@ -0,0 +1,28 @@ >> +// SPDX-License-Identifier: GPL-2.0-only >> +/* >> + * Base file contains the default implementations. >> + * These are defined as __weak so that arch may define >> + * strong symbols to override. > > But there's no arch doing that, right? It looks like overcomplication > with no benefit. > > There's just ~50 drivers defining weak symbols, so this is not a > common practice. I think it would be much simpler for the arch people > to simply write their own driver controlling cpu_preferred_mask, > rather than tweaking your code. > s390 folks asked for explicit hooks since they have some of the info coming from HW w.r.t to vertical high/vertical low etc. So i have designed it that way. (I know code is not there yet) If each arch writes its own driver, wouldn't that lead to - code duplication as each arch more or less may have to do same. - each arch has to catch up any improvements that happens to default monitor. - each arch has to honor design construct and not violate it. - kconfig puzzles, to choose generic or arch specific ones etc. If it makes sense, - I can make it as strong symbols for now. - when the arch specific implementations arrive, can make it as __weak to accommodate that.