On Tue, Nov 08, 2016 at 07:31:45AM +0100, Ingo Molnar wrote: > So the point I tried to make is that to people doing -stable > backporting decisions this description you just gave is much more > valuable than the previous changelog.
Ok, how's that below? I've integrated the gist of it in the commit message: --- From: Yazen Ghannam <yazen.ghan...@amd.com> Date: Tue, 1 Nov 2016 11:51:02 -0500 Subject: [PATCH] x86/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. Signed-off-by: Yazen Ghannam <yazen.ghan...@amd.com> Tested-by: Borislav Petkov <b...@suse.de> Cc: Aravind Gopalakrishnan <aravindksg.l...@gmail.com> Cc: <sta...@vger.kernel.org> # v4.4.. Cc: x86-ml <x...@kernel.org> Link: http://lkml.kernel.org/r/1478019063-2632-1-git-send-email-yazen.ghan...@amd.com Fixes: 3849e91f571d ("x86/AMD: Fix last level cache topology for AMD Fam17h systems") [ Boris: cleanup and extend commit message. ] Signed-off-by: Borislav Petkov <b...@suse.de> --- 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 b81fe2d63e15..1e81a37c034e 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 } -- 2.10.0 SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --
