Re: [PATCH 2/3] x86/topology: Fix AMD core count

[Huang Rui <ray.huang@amd.com>]

On Mon, Mar 21, 2016 at 11:07:44AM +0800, Huang Rui wrote:
> On Fri, Mar 18, 2016 at 05:41:01PM +0100, Borislav Petkov wrote:
> > On Fri, Mar 18, 2016 at 04:03:47PM +0100, Peter Zijlstra wrote:
> > > It turns out AMD gets x86_max_cores wrong when there are compute
> > > units.
> > > 
> > > The issue is that Linux assumes:
> > > 
> > > 	nr_logical_cpus = nr_cores * nr_siblings
> > > 
> > > But AMD reports its CU unit as 2 cores, but then sets num_smp_siblings
> > > to 2 as well.
> > > 
> > > Cc: Ingo Molnar <mingo@kernel.org>
> > > Cc: Borislav Petkov <bp@alien8.de>
> > > Cc: Thomas Gleixner <tglx@linutronix.de>
> > > Cc: Andreas Herrmann <aherrmann@suse.com>
> > > Reported-by: Xiong Zhou <jencce.kernel@gmail.com>
> > > Fixes: 1f12e32f4cd5 ("x86/topology: Create logical package id")
> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > > Link: http://lkml.kernel.org/r/20160317095220.GO6344@twins.programming.kicks-ass.net
> > > ---
> > >  arch/x86/kernel/cpu/amd.c |    8 ++++----
> > >  arch/x86/kernel/smpboot.c |   11 ++++++-----
> > >  2 files changed, 10 insertions(+), 9 deletions(-)
> > > 
> > > --- a/arch/x86/kernel/cpu/amd.c
> > > +++ b/arch/x86/kernel/cpu/amd.c
> > > @@ -313,9 +313,9 @@ static void amd_get_topology(struct cpui
> > >  		node_id = ecx & 7;
> > >  
> > >  		/* get compute unit information */
> > > -		smp_num_siblings = ((ebx >> 8) & 3) + 1;
> > > +		cores_per_cu = smp_num_siblings = ((ebx >> 8) & 3) + 1;
> > > +		c->x86_max_cores /= smp_num_siblings;
> > >  		c->compute_unit_id = ebx & 0xff;
> > > -		cores_per_cu += ((ebx >> 8) & 3);
> > >  	} else if (cpu_has(c, X86_FEATURE_NODEID_MSR)) {
> > >  		u64 value;
> > >  
> > > @@ -331,8 +331,8 @@ static void amd_get_topology(struct cpui
> > >  		u32 cus_per_node;
> > >  
> > >  		set_cpu_cap(c, X86_FEATURE_AMD_DCM);
> > > -		cores_per_node = c->x86_max_cores / nodes_per_socket;
> > > -		cus_per_node = cores_per_node / cores_per_cu;
> > > +		cus_per_node = c->x86_max_cores / nodes_per_socket;
> > > +		cores_per_node = cus_per_node * cores_per_cu;
> > >  
> > >  		/* store NodeID, use llc_shared_map to store sibling info */
> > >  		per_cpu(cpu_llc_id, cpu) = node_id;
> > 
> > Looks ok to me, however it probably would be prudent if AMD tested it on
> > a bunch of machines just to make sure we don't break anything else. I'm
> > thinking F15h and F16h, something big...
> > 
> > Rui, can you find some time to run this one please?
> > 
> > Look at before/after info in /proc/cpuinfo, topology in sysfs and dmesg
> > before and after might be useful too.
> > 
> 
> OK, we will find some fam15h, fam16h platforms to verify it. Please
> wait for my feedback.
> 
> But I am confused with c->x86_max_cores /= smp_num_siblings, what is
> the real meaning of c->x86_max_cores here for AMD, the whole compute
> unit numbers per socket?
> 
> + Sherry, for her awareness.
> 

I quickly applied this patch on tip/master with on a fam15h machine.
The issue is still existed, only one core can be detected.

processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 21
model           : 2
model name      : AMD Opteron(tm) Processor 6386 SE
stepping        : 0
microcode       : 0x6000822
cpu MHz         : 2792.882
cache size      : 2048 KB
fpu             : yes
fpu_exception   : yes
cpuid level     : 13
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl nonstop_tsc extd_apicid aperfmperf eagerfpu pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 popcnt aes xsave avx f16c lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs xop skinit wdt lwp fma4 tce nodeid_msr tbm topoext perfctr_core perfctr_nb cpb hw_pstate vmmcall bmi1 arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold
bugs            : fxsave_leak sysret_ss_attrs
bogomips        : 5585.76
TLB size        : 1536 4K pages
clflush size    : 64
cache_alignment : 64
address sizes   : 48 bits physical, 48 bits virtual
power management: ts ttp tm 100mhzsteps hwpstate cpb eff_freq_ro


Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                1
On-line CPU(s) list:   0
Thread(s) per core:    1
Core(s) per socket:    1
Socket(s):             1
Vendor ID:             AuthenticAMD
CPU family:            21
Model:                 2
Stepping:              0
CPU MHz:               2792.882
BogoMIPS:              5585.76
Virtualization:        AMD-V
L1d cache:             16K
L1i cache:             64K
L2 cache:              2048K
L3 cache:              6144K

Thanks,
Rui