From: Srikar Dronamraju <srikar@linux.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
Ben Segall <bsegall@google.com>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Ingo Molnar <mingo@kernel.org>,
Juri Lelli <juri.lelli@redhat.com>,
K Prateek Nayak <kprateek.nayak@amd.com>,
Madhavan Srinivasan <maddy@linux.ibm.com>,
Mel Gorman <mgorman@suse.de>,
Michael Ellerman <mpe@ellerman.id.au>,
Nicholas Piggin <npiggin@gmail.com>,
Shrikanth Hegde <sshegde@linux.ibm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Swapnil Sapkal <swapnil.sapkal@amd.com>,
Thomas Huth <thuth@redhat.com>,
Valentin Schneider <vschneid@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
virtualization@lists.linux.dev,
Ilya Leoshkevich <iii@linux.ibm.com>,
Beata Michalska <beata.michalska@arm.com>
Subject: Re: [PATCH 08/17] sched/core: Implement CPU soft offline/online
Date: Sat, 6 Dec 2025 00:24:51 +0530 [thread overview]
Message-ID: <aTMqeylKyRwS7mn_@linux.ibm.com> (raw)
In-Reply-To: <20251205160326.GF2528459@noisy.programming.kicks-ass.net>
* Peter Zijlstra <peterz@infradead.org> [2025-12-05 17:03:26]:
Hi Peter,
>
> What happens if you then offline one of these softoffline CPUs? Doesn't
> that do sched_cpu_deactivate() again?
>
> Also, the way this seems to use softoffline_mask is as a hidden argument
> to sched_cpu_{de,}activate() instead of as an actual mask.
>
> Moreover, there does not seem to be any sort of serialization vs
> concurrent set_cpu_softoffline() callers. At the very least
> update_group_capacity() would end up with indeterminate results.
>
To serialize soft_offline with actual offline, can we take cpu_maps_update_begin() / cpu_maps_update_done
> This all doesn't look 'robust'.
I figured out when Shrikanth Hegde reported a warning to me today evening.
Basically pin a task to CPU, and then run workload so that the load causes steal and then do a cpu offline
Pinning just causes the window to be sure enough to hit the case easily.
[ 804.464298] ------------[ cut here ]------------
[ 804.464325] CPU capacity asymmetry not supported on SMT
[ 804.464341] WARNING: CPU: 575 PID: 2926 at kernel/sched/topology.c:1677 sd_init+0x428/0x494
[ 804.464355] Modules linked in: nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 bonding tls rfkill ip_set nf_tables nfnetlink sunrpc pseries_rng vmx_crypto drm drm_panel_orientation_quirks xfs sd_mod sg ibmvscsi scsi_transport_srp ibmveth pseries_wdt dm_mirror dm_region_hash dm_log dm_mod fuse
[ 804.464409] CPU: 575 UID: 0 PID: 2926 Comm: cpuhp/575 Kdump: loaded Not tainted 6.18.0-master+ #15 VOLUNTARY
[ 804.464415] Hardware name: IBM,9080-HEU Power11 (architected) 0x820200 0xf000007 of:IBM,FW1110.00 (OK1110_066) hv:phyp pSeries
[ 804.464420] NIP: c000000000215c4c LR: c000000000215c48 CTR: 00000000005d54a0
[ 804.464425] REGS: c00001801cfff3c0 TRAP: 0700 Not tainted (6.18.0-master+)
[ 804.464429] MSR: 8000000000029033 <SF,EE,ME,IR,DR,RI,LE> CR: 28828228 XER: 0000000c
[ 804.464441] CFAR: c000000000171988 IRQMASK: 0
GPR00: c000000000215c48 c00001801cfff660 c000000001c28100 000000000000002b
GPR04: 0000000000000000 c00001801cfff470 c00001801cfff468 000001fff1280000
GPR08: 0000000000000027 0000000000000000 0000000000000000 0000000000000001
GPR12: c00001ffe182ffa8 c00001fff5d43b00 c00001804e999548 0000000000000000
GPR16: 0000000000000000 c0000000015732e8 c00000000153f380 c00000012b337c18
GPR20: c000000002edb660 0000000000000239 0000000000000004 c000018029a26200
GPR24: 0000000000000000 c0000000029787c8 0000000000000002 c00000012b337c00
GPR28: c00001804e7cb948 c000000002ee06d0 c00001804e7cb800 c0000000029787c8
[ 804.464491] NIP [c000000000215c4c] sd_init+0x428/0x494
[ 804.464496] LR [c000000000215c48] sd_init+0x424/0x494
[ 804.464501] Call Trace:
[ 804.464504] [c00001801cfff660] [c000000000215c48] sd_init+0x424/0x494 (unreliable)
[ 804.464511] [c00001801cfff740] [c000000000226fd8] build_sched_domains+0x1c0/0x938
[ 804.464517] [c00001801cfff850] [c000000000228f98] partition_sched_domains_locked+0x4a8/0x688
[ 804.464523] [c00001801cfff940] [c000000000229244] partition_sched_domains+0x5c/0x84
[ 804.464528] [c00001801cfff990] [c00000000031a020] rebuild_sched_domains_locked+0x1d8/0x260
[ 804.464536] [c00001801cfff9f0] [c00000000031dde4] cpuset_handle_hotplug+0x564/0x728
[ 804.464542] [c00001801cfffd80] [c0000000001d9fa8] sched_cpu_activate+0x2d4/0x2dc
[ 804.464549] [c00001801cfffde0] [c00000000017567c] cpuhp_invoke_callback+0x26c/0xb20
[ 804.464556] [c00001801cfffec0] [c000000000177554] cpuhp_thread_fun+0x210/0x2e8
[ 804.464561] [c00001801cffff40] [c0000000001c1640] smpboot_thread_fn+0x200/0x2c0
[ 804.464568] [c00001801cffff90] [c0000000001b5758] kthread+0x134/0x164
[ 804.464575] [c00001801cffffe0] [c00000000000ded8] start_kernel_thread+0x14/0x18
[ 804.464581] Code: 4082fe5c 3d420120 894a2525 2c0a0000 4082fe4c 3c62ff95 39200001 3d420120 38639830 992a2525 4bf5bcbd 60000000 <0fe00000> 813e003c 4bfffe24 60000000
[ 804.464598] ---[ end trace 0000000000000000 ]---
But this warning will still remain even if we take the cpu_maps_update_begin.
This comes due to
WARN_ONCE((sd->flags & (SD_SHARE_CPUCAPACITY | SD_ASYM_CPUCAPACITY)) ==
(SD_SHARE_CPUCAPACITY | SD_ASYM_CPUCAPACITY),
"CPU capacity asymmetry not supported on SMT\n");
which was recently added by
Commit c744dc4ab58d ("sched/topology: Rework CPU capacity asymmetry detection")
Is there a way to tweak this WARN_ONCE?
--
Thanks and Regards
Srikar Dronamraju
next prev parent reply other threads:[~2025-12-05 18:55 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-04 17:53 [PATCH 00/17] Steal time based dynamic CPU resource management Srikar Dronamraju
2025-12-04 17:53 ` [PATCH 01/17] sched/fair: Enable group_asym_packing in find_idlest_group Srikar Dronamraju
2025-12-04 17:53 ` [PATCH 02/17] powerpc/lpar: Reorder steal accounting calculation Srikar Dronamraju
2025-12-04 17:53 ` [PATCH 03/17] pseries/lpar: Process steal metrics Srikar Dronamraju
2025-12-04 17:53 ` [PATCH 04/17] powerpc/smp: Add num_available_cores callback for smp_ops Srikar Dronamraju
2025-12-04 17:53 ` [PATCH 05/17] pseries/smp: Query and set entitlements Srikar Dronamraju
2025-12-04 17:53 ` [PATCH 06/17] powerpc/smp: Delay processing steal time at boot Srikar Dronamraju
2025-12-04 17:53 ` [PATCH 07/17] sched/core: Set balance_callback only if CPU is dying Srikar Dronamraju
2025-12-04 17:53 ` [PATCH 08/17] sched/core: Implement CPU soft offline/online Srikar Dronamraju
2025-12-05 16:03 ` Peter Zijlstra
2025-12-05 18:54 ` Srikar Dronamraju [this message]
2025-12-05 16:07 ` Peter Zijlstra
2025-12-05 18:57 ` Srikar Dronamraju
2025-12-04 17:53 ` [PATCH 09/17] powerpc/smp: Implement arch_scale_cpu_capacity for shared LPARs Srikar Dronamraju
2025-12-04 17:53 ` [PATCH 10/17] powerpc/smp: Define arch_update_cpu_topology " Srikar Dronamraju
2025-12-04 17:53 ` [PATCH 11/17] pseries/smp: Create soft offline infrastructure for Powerpc " Srikar Dronamraju
2025-12-04 17:54 ` [PATCH 12/17] pseries/smp: Trigger softoffline based on steal metrics Srikar Dronamraju
2025-12-04 17:54 ` [PATCH 13/17] pseries/smp: Account cores when triggering softoffline Srikar Dronamraju
2025-12-04 17:54 ` [PATCH 14/17] powerpc/smp: Assume preempt if CPU is inactive Srikar Dronamraju
2025-12-04 17:54 ` [PATCH 15/17] pseries/hotplug: Update available_cores on a dlpar event Srikar Dronamraju
2025-12-04 17:54 ` [PATCH 16/17] pseries/smp: Allow users to override steal thresholds Srikar Dronamraju
2025-12-04 17:54 ` [PATCH 17/17] pseries/lpar: Add debug interface to set steal interval Srikar Dronamraju
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