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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 <bp@suse.de>
Signed-off-by: Yazen Ghannam <Yazen.Ghannam@amd.com>
[ Cleaned up and extended the commit message. ]
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@vger.kernel.org> # v4.4..
Cc: Aravind Gopalakrishnan <aravindksg.lkml@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Fixes: 3849e91f57 ("x86/AMD: Fix last level cache topology for AMD Fam17h systems")
Link: http://lkml.kernel.org/r/20161108083506.rvqb5h4chrcptj7d@pd.tnic
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Yazen Ghannam 2016-11-08 09:35:06 +01:00 committed by Ingo Molnar
parent e8a6123e9e
commit b0b6e86846
1 changed files with 1 additions and 5 deletions
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6
arch/x86/kernel/cpu/amd.c
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@ -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
}