Messages in this thread | | | Subject | Re: AMD Bulldozer topology regression since 4.6 | From | Brice Goglin <> | Date | Tue, 3 Jan 2017 11:49:38 +0100 |
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Le 29/11/2016 22:02, Brice Goglin a écrit : > Le 29/11/2016 20:39, Borislav Petkov a écrit : >> Does that fix it? >> >> Patch is against latest tip/master because we have some more changes in >> that area. > I tested the second patch on top of 4.8.11, it brings core_id back to > where it was before 4.6, thanks. > > Reported-and-tested-by: Brice Goglin <Brice.Goglin@inria.fr>
Hello Borislav Are you pushing this fix to Linus soon? We received several bug reports on our side about dual-core compute units being exposed as a dual-threaded single-cores in sysfs. Thanks Brice
> However thread_siblings isn't back to where it was in 4.5. Now we have a > single bit in each thread_siblings mask. That's correct with respect to > the sysfs topology documentation. In 4.5, there were two bits (one for > each core of the compute unit), which was wrong (cores with different > core_ids shouldn't appear in each other thread_siblings). I assumed that > these processors had to break the sysfs topology documentation to expose > the concept of "dual-core compute-unit" which somehow sits between > hyperthreading and dual-core. > > I personally do not care much about this regression, not sure about > other user-space tools? > > Another minor related change: /proc/cpuinfo shows "cpu cores : 16" > instead of "8". > > Brice > > >> --- >> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c >> index 4daad1e39352..a070d7b0a133 100644 >> --- a/arch/x86/kernel/cpu/amd.c >> +++ b/arch/x86/kernel/cpu/amd.c >> @@ -305,15 +305,7 @@ static void amd_get_topology(struct cpuinfo_x86 *c) >> >> /* get information required for multi-node processors */ >> if (boot_cpu_has(X86_FEATURE_TOPOEXT)) { >> - u32 eax, ebx, ecx, edx; >> - >> - cpuid(0x8000001e, &eax, &ebx, &ecx, &edx); >> - node_id = ecx & 7; >> - >> - /* get compute unit information */ >> - smp_num_siblings = ((ebx >> 8) & 3) + 1; >> - c->x86_max_cores /= smp_num_siblings; >> - c->cpu_core_id = ebx & 0xff; >> + node_id = cpuid_ecx(0x8000001e) & 7; >> >> /* >> * We may have multiple LLCs if L3 caches exist, so check if we >> --- >> >> Just in case, I have one against Linus' master too: >> >> --- >> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c >> index 1e81a37c034e..19f50a9d6b42 100644 >> --- a/arch/x86/kernel/cpu/amd.c >> +++ b/arch/x86/kernel/cpu/amd.c >> @@ -305,15 +305,7 @@ static void amd_get_topology(struct cpuinfo_x86 *c) >> >> /* get information required for multi-node processors */ >> if (boot_cpu_has(X86_FEATURE_TOPOEXT)) { >> - u32 eax, ebx, ecx, edx; >> - >> - cpuid(0x8000001e, &eax, &ebx, &ecx, &edx); >> - node_id = ecx & 7; >> - >> - /* get compute unit information */ >> - smp_num_siblings = ((ebx >> 8) & 3) + 1; >> - c->x86_max_cores /= smp_num_siblings; >> - c->cpu_core_id = ebx & 0xff; >> + node_id = cpuid_ecx(0x8000001e) & 7; >> } else if (cpu_has(c, X86_FEATURE_NODEID_MSR)) { >> u64 value; >> --- >>
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