On 11/07/2016 11:19 AM, Thomas Gleixner wrote:
On Wed, 2 Nov 2016, Charles (Chas) Williams wrote:
On 11/02/2016 08:25 AM, Sebastian Andrzej Siewior wrote:
I am not sure if this a race with the new hotplug code or something that was
always there. Both (M. Vefa Bicakc and Charles) say that the box boots
sometimes fine (without the patch). smp_store_boot_cpu_info() should have
run
before the notofoert and thus should have set the info properly. However I
got
the following bootlog from Charles with this patch:
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.
max_physical_pkg_id gets initialized via:
cpus = boot_cpu_data.x86_max_cores;
max_physical_pkg_id = DIV_ROUND_UP(MAX_LOCAL_APIC, ncpus);
What's the value of boot_cpu_data.x86_max_cores and MAX_LOCAL_APIC?
I have discovered that that is not the problem. smp_init_package_map()
is calculating the physical core id using the following:
for_each_present_cpu(cpu) {
unsigned int apicid = apic->cpu_present_to_apicid(cpu);
...
if (!topology_update_package_map(apicid, cpu))
continue;
...
int topology_update_package_map(unsigned int apicid, unsigned int cpu)
{
unsigned int new, pkg = apicid >> boot_cpu_data.x86_coreid_bits;
But later when the secondary CPU's are identified they use a different
calculation using the local APIC ID from the CPU's registers:
static void generic_identify(struct cpuinfo_x86 *c)
...
if (c->cpuid_level >= 0x00000001) {
c->initial_apicid = (cpuid_ebx(1) >> 24) & 0xFF;
...
c->phys_proc_id = c->initial_apicid;
So at the end of identify_cpu() when the boot/hotplug assignment is
put back:
c->logical_proc_id = topology_phys_to_logical_pkg(c->phys_proc_id);
topology_phys_to_logical_pkg() is returning an invalid logical processor
since one isn't configured.
It's not clear to me what the right thing to do is or which is right.
