On 11/03/2016 01:47 PM, Sebastian Andrzej Siewior wrote:
On 2016-11-02 18:47:49 [-0400], Charles (Chas) Williams wrote:
I don't this this is a race. Here is some debugging from the two CPU VM
(2 sockets, 1 core per socket). In identify_cpu() we have:
/* The boot/hotplug time assigment got cleared, restore it */
c->logical_proc_id = topology_phys_to_logical_pkg(c->phys_proc_id);
The values just after this:
[ 0.228306] identify_cpu: c ffff88023fd0a040 logical_proc_id 65535
c->phys_proc_id 2
So what's interesting here, is the phys_proc_id of 2 for CPU1:
int topology_phys_to_logical_pkg(unsigned int phys_pkg)
{
if (phys_pkg >= max_physical_pkg_id)
return -1;
return physical_to_logical_pkg[phys_pkg];
}
And we happen to know the max_physical_pkg_id is 2 in this case.
So apparently, topology_phys_to_logical_pkg() returns -1 and it gets
assigned to the logical_proc_id.
I don't know why the CPU's phys_proc_id is 2.
This is the physical ID. You have two logical IDs (on your two sockets
machine). What is max_physical_pkg_id? In order to get that -1 you would
have to max_physical_pkg_id of 1 but code does
max_physical_pkg_id = DIV_ROUND_UP(MAX_LOCAL_APIC, ncpus);
and I would be a little surprised if this is 1.
Sebastian
The initial CPU boots and is identified:
[ 0.009018] identify_boot_cpu
[ 0.009174] generic_identify: phys_proc_id is now 0
...
[ 0.009427] identify_cpu: before c ffffffff81ae2680 logical_proc_id 0
c->phys_proc_id 0
[ 0.009506] identify_cpu: after c ffffffff81ae2680 logical_proc_id 65535
c->phys_proc_id 0
So, this is fine because the APIC hasn't been scanned yet. APIC
now gets scanned:
[ 0.015789] smpboot: APIC(0) Converting physical 0 to logical package 0, cpu
0 (ffff88023fc0a040)
[ 0.015794] smpboot: APIC(1) Converting physical 1 to logical package 1, cpu
1 (ffff88023fd0a040)
[ 0.015797] smpboot: Max logical packages: 2
So, at this point, I think everything is correct. But now the secondary
CPU's "boot":
[ 0.236569] identify_secondary_cpu
[ 0.236620] generic_identify: phys_proc_id is now 2
[ 0.236745] identify_cpu: before c ffff88023fd0a040 logical_proc_id 65535
c->phys_proc_id 2
[ 0.236747] identify_cpu: after c ffff88023fd0a040 logical_proc_id 65535
c->phys_proc_id 2
So, APIC discovered I have a cpu 0 and 1 but generic_identify() is called
my second CPU, 2. This is >= max_physical_pkg_id, so it is going to get
set to -1.
The comment at the end of identfy_cpu() says:
/* The boot/hotplug time assigment got cleared, restore it */
So, logical_proc_id being wrong here before restoration doesn't bother
me since I assume something in booting the secondary CPU's clears any
existing cpu data.
I know detect_extended_topology() is likely being called for both CPU's
and getting the right values (checking this now). I don't know why
generic_identify() is resetting this value.
