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 <[email protected]> > > Cc: Borislav Petkov <[email protected]> > > Cc: Thomas Gleixner <[email protected]> > > Cc: Andreas Herrmann <[email protected]> > > Reported-by: Xiong Zhou <[email protected]> > > Fixes: 1f12e32f4cd5 ("x86/topology: Create logical package id") > > Signed-off-by: Peter Zijlstra (Intel) <[email protected]> > > Link: > > http://lkml.kernel.org/r/[email protected] > > --- > > 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. Thanks, Rui
