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Subject[tip:x86/urgent] x86/smpboot: Do not use smp_num_siblings in __max_logical_packages calculation
Commit-ID:  947134d9b00f342415af7eddd42a5fce7262a1b9
Author: Prarit Bhargava <>
AuthorDate: Mon, 4 Dec 2017 11:45:21 -0500
Committer: Thomas Gleixner <>
CommitDate: Thu, 7 Dec 2017 10:28:22 +0100

x86/smpboot: Do not use smp_num_siblings in __max_logical_packages calculation

Documentation/x86/topology.txt defines smp_num_siblings as "The number of
threads in a core". Since commit bbb65d2d365e ("x86: use cpuid vector 0xb
when available for detecting cpu topology") smp_num_siblings is the
maximum number of threads in a core. If Simultaneous MultiThreading
(SMT) is disabled on a system, smp_num_siblings is 2 and not 1 as

Use topology_max_smt_threads(), which contains the active numer of threads,
in the __max_logical_packages calculation.

On a single socket, single core, single thread system __max_smt_threads has
not been updated when the __max_logical_packages calculation happens, so its
zero which makes the package estimate fail. Initialize it to one, which is
the minimum number of threads on a core.

[ tglx: Folded the __max_smt_threads fix in ]

Fixes: b4c0a7326f5d ("x86/smpboot: Fix __max_logical_packages estimate")
Reported-by: Jakub Kicinski <>
Signed-off-by: Prarit Bhargava <
Signed-off-by: Thomas Gleixner <>
Tested-by: Jakub Kicinski <>
Cc: ""
Cc: Clark Williams <>
arch/x86/kernel/smpboot.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 05a97d5..35cb20994 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -106,7 +106,7 @@ EXPORT_SYMBOL(__max_logical_packages);
static unsigned int logical_packages __read_mostly;

/* Maximum number of SMT threads on any online core */
-int __max_smt_threads __read_mostly;
+int __read_mostly __max_smt_threads = 1;

/* Flag to indicate if a complete sched domain rebuild is required */
bool x86_topology_update;
@@ -1304,7 +1304,7 @@ void __init native_smp_cpus_done(unsigned int max_cpus)
* Today neither Intel nor AMD support heterogenous systems so
* extrapolate the boot cpu's data to all packages.
- ncpus = cpu_data(0).booted_cores * smp_num_siblings;
+ ncpus = cpu_data(0).booted_cores * topology_max_smt_threads();
__max_logical_packages = DIV_ROUND_UP(nr_cpu_ids, ncpus);
pr_info("Max logical packages: %u\n", __max_logical_packages);

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