Commit-ID: b0b6e86846093c5f8820386bc01515f857dd8faa Gitweb: http://git.kernel.org/tip/b0b6e86846093c5f8820386bc01515f857dd8faa Author: Yazen Ghannam <[email protected]> AuthorDate: Tue, 8 Nov 2016 09:35:06 +0100 Committer: Ingo Molnar <[email protected]> CommitDate: Wed, 9 Nov 2016 17:06:08 +0100
x86/cpu/AMD: Fix cpu_llc_id for AMD Fam17h systems cpu_llc_id (Last Level Cache ID) derivation on AMD Fam17h has an underflow bug when extracting the socket_id value. It starts from 0 so subtracting 1 from it will result in an invalid value. This breaks scheduling topology later on since the cpu_llc_id will be incorrect. For example, the the cpu_llc_id of the *other* CPU in the loops in set_cpu_sibling_map() underflows and we're generating the funniest thread_siblings masks and then when I run 8 threads of nbench, they get spread around the LLC domains in a very strange pattern which doesn't give you the normal scheduling spread one would expect for performance. Other things like EDAC use cpu_llc_id so they will be b0rked too. So, the APIC ID is preset in APICx020 for bits 3 and above: they contain the core complex, node and socket IDs. The LLC is at the core complex level so we can find a unique cpu_llc_id by right shifting the APICID by 3 because then the least significant bit will be the Core Complex ID. Tested-by: Borislav Petkov <[email protected]> Signed-off-by: Yazen Ghannam <[email protected]> [ Cleaned up and extended the commit message. ] Signed-off-by: Borislav Petkov <[email protected]> Acked-by: Thomas Gleixner <[email protected]> Cc: <[email protected]> # v4.4.. Cc: Aravind Gopalakrishnan <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Fixes: 3849e91f571d ("x86/AMD: Fix last level cache topology for AMD Fam17h systems") Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/kernel/cpu/amd.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index b81fe2d..1e81a37 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -347,7 +347,6 @@ static void amd_detect_cmp(struct cpuinfo_x86 *c) #ifdef CONFIG_SMP unsigned bits; int cpu = smp_processor_id(); - unsigned int socket_id, core_complex_id; bits = c->x86_coreid_bits; /* Low order bits define the core id (index of core in socket) */ @@ -365,10 +364,7 @@ static void amd_detect_cmp(struct cpuinfo_x86 *c) if (c->x86 != 0x17 || !cpuid_edx(0x80000006)) return; - socket_id = (c->apicid >> bits) - 1; - core_complex_id = (c->apicid & ((1 << bits) - 1)) >> 3; - - per_cpu(cpu_llc_id, cpu) = (socket_id << 3) | core_complex_id; + per_cpu(cpu_llc_id, cpu) = c->apicid >> 3; #endif }
