linux-kernel - Re: [PATCH v4 1/2] sched/topology: improve topology_span

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Message-ID: <a5da2e4d-c042-4d01-bfc3-f50ca674247b@amd.com>
Date: Tue, 10 Jun 2025 17:03:14 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Leon Romanovsky <leon@...nel.org>, Steve Wahl <steve.wahl@....com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
 linux-kernel@...r.kernel.org, Vishal Chourasia <vishalc@...ux.ibm.com>,
 samir <samir@...ux.ibm.com>, Naman Jain <namjain@...ux.microsoft.com>,
 Saurabh Singh Sengar <ssengar@...ux.microsoft.com>, srivatsa@...il.mit.edu,
 Michael Kelley <mhklinux@...look.com>, Russ Anderson <rja@....com>,
 Dimitri Sivanich <sivanich@....com>
Subject: Re: [PATCH v4 1/2] sched/topology: improve topology_span_sane speed

Hello Leon,

On 6/10/2025 4:37 PM, Leon Romanovsky wrote:

[..snip..]

>>   
>> +	if (WARN_ON(!topology_span_sane(cpu_map)))
>> +		goto error;
> 
> Hi,
> 
> This WARN_ON() generate the following splat in our regression over VMs.> 
>   [    0.408379] ------------[ cut here ]------------
>   [    0.409097] WARNING: CPU: 0 PID: 1 at kernel/sched/topology.c:2486 build_sched_domains+0xe67/0x13a0
>   [    0.410797] Modules linked in:
>   [    0.411453] CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.16.0-rc1_for_upstream_min_debug_2025_06_09_14_44 #1 NONE
>   [    0.413353] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
>   [    0.415440] RIP: 0010:build_sched_domains+0xe67/0x13a0
>   [    0.416458] Code: ff ff 8b 6c 24 08 48 8b 44 24 68 65 48 2b 05 60 24 d0 01 0f 85 03 05 00 00 48 83 c4 70 89 e8 5b 5d 41 5c 41 5d 41 5e 41 5f c3 <0f> 0b e9 65 fe ff ff 48 c7 c7 28 fb 08 82 4c 89 44 24 28 c6 05 e4
>   [    0.417662] RSP: 0000:ffff8881002efe30 EFLAGS: 00010202
>   [    0.418686] RAX: 00000000ffffff01 RBX: 0000000000000002 RCX: 00000000ffffff01
>   [    0.419982] RDX: 00000000fffffff6 RSI: 0000000000000300 RDI: ffff888100047168
>   [    0.421166] RBP: 0000000000000000 R08: ffff888100047168 R09: 0000000000000000
>   [    0.422514] R10: ffffffff830dee80 R11: 0000000000000000 R12: ffff888100047168
>   [    0.423820] R13: 0000000000000002 R14: ffff888100193480 R15: ffff888380030f40
>   [    0.425164] FS:  0000000000000000(0000) GS:ffff8881b9b76000(0000) knlGS:0000000000000000
>   [    0.426751] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   [    0.427832] CR2: ffff88843ffff000 CR3: 000000000282c001 CR4: 0000000000370eb0
>   [    0.428818] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>   [    0.430131] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>   [    0.431429] Call Trace:
>   [    0.431983]  <TASK>
>   [    0.432500]  sched_init_smp+0x32/0xa0
>   [    0.433069]  ? stop_machine+0x2c/0x40
>   [    0.433821]  kernel_init_freeable+0xf5/0x260
>   [    0.434682]  ? rest_init+0xc0/0xc0
>   [    0.435399]  kernel_init+0x16/0x120
>   [    0.436140]  ret_from_fork+0x5e/0xd0
>   [    0.436817]  ? rest_init+0xc0/0xc0
>   [    0.437526]  ret_from_fork_asm+0x11/0x20
>   [    0.438335]  </TASK>
>   [    0.438841] ---[ end trace 0000000000000000 ]---

Would it be possible for you to boot the guest with "sched_verbose" in
kernel cmdline and attach the full dmesg? Thanks in advance.

-- 
Thanks and Regards,
Prateek

> 
> Thanks
> 
>> +
>>   	/* Build the groups for the domains */
>>   	for_each_cpu(i, cpu_map) {
>>   		for (sd = *per_cpu_ptr(d.sd, i); sd; sd = sd->parent) {
>> -- 
>> 2.26.2
>>