Messages in this thread | | | Date | Wed, 8 May 2024 10:38:26 +0200 | Subject | Re: Early boot regression from f0551af0213 ("x86/topology: Ignore non-present APIC IDs in a present package") | From | "Linux regression tracking (Thorsten Leemhuis)" <> |
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H! Lyude, Thomas, what's the status here? From here it looks like we were close to a fix, but then it turned out to be a bad fix -- and afterwards nothing much seems to have happened. Did it fall through the cracks, or was this already fixed and I just missed that?
Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
On 02.05.24 12:33, Mario Limonciello wrote: > On 4/25/2024 16:42, Thomas Gleixner wrote: >> On Thu, Apr 25 2024 at 11:56, Lyude Paul wrote: >>> On Thu, 2024-04-25 at 04:11 +0200, Thomas Gleixner wrote: >>>> >>>> Can you please boot a kernel with the commit in question reverted and >>>> add 'possible_cpus=8' to the kernel command line? >>>> >>>> In theory this should fail too. >>> >>> Yep - tried booting a kernel with f0551af0213 reverted and >>> possible_cpus=8, it definitely looks like that crashes things as well >>> in the same way. >> >> Good. That means it's a problem which existed before but went unnoticed. >> >>> Also - it scrolled off the screen before I had a chance to write it >>> down, but I'm -fairly- sure I saw some sort of complaint about "16 [or >>> some double digit number] processors exceeds max number of 8". Which >>> is quite interesting, as this is definitely just a quad core ryzen >>> processor with hyperthreading - so there should only be 8 threads. >> >> Right, that's what we saw with the debug patch. The ACPI/MADT table >> is clearly bonkers. The effect of it is that it pretends that the system >> has 16 possible CPUs: >> >> [ 0.089381] CPU topo: Allowing 8 present CPUs plus 8 hotplug CPUs >> >> Which in turn changes the sizing of the per CPU data and affects some >> other details which depend on the number of possible CPUs. > > At least this aspect of this I suspect is caused by commit > fed8d8773b8ea68ad99d9eee8c8343bef9da2c2c. > > If you try reverting that I expect the "hotplug CPUs" disappear. > >> >> But that should not matter at all because the system scaling should be >> sufficient with 8 CPUs, but it does not for some completely non-obvious >> reasons. >> >> Can you please try to increase possible_cpus=N on the command line one >> by one and check when it actually starts to "work" again. >> >> One other thing to try is to boot with 'possible_cpus=8' and >> 'intremap=off' and see whether that makes a difference. >> >> I really have no idea where to look and not having the early boot >> messages in case of the fail is not helpful as I can't add meaningful >> debug to it. >> >> I just checked: the motherboard has a serial port, so it would be >> extremly helpful to hook up a serial cable to this thing and enable >> serial console on the kernel command line. That way we might eventually >> see information which is emitted before it fails to validate the timer >> interrupt. >>
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