Re: [PATCH v4 1/2] sched/topology: improve topology_span_sane speed

[Leon Romanovsky <leon@kernel.org>]

On Tue, Jun 10, 2025 at 05:03:14PM +0530, K Prateek Nayak wrote:
> 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.

I'll try, but can't promise due to how this kernel is been running in
our systems.

Thanks

> 
> -- 
> 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
> > > 
>