Messages in this thread | | | Subject | Re: [PATCH 4/7] perf: Check if HT is supported and enabled | From | Lin Ming <> | Date | Wed, 05 Jan 2011 13:45:20 +0800 |
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On Tue, 2011-01-04 at 21:52 +0800, Stephane Eranian wrote: > On Tue, Jan 4, 2011 at 2:44 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > > On Tue, 2011-01-04 at 14:38 +0100, Stephane Eranian wrote: > >> My solution at the time (2.6.30) was to do: > >> ht_enabled = cpumask_weight(__get_cpu_var(cpu_sibling_map)) > 1; > > > > Won't that report a machine a HT disabled when you offline a sibling? > > I think you're right. I was not dealing with hotplug CPU. > > > Which kinda defeats the purpose of our usage here, since we need to know > > it before either sibling comes online. > > Then, it seems the only hope is to peek at a MSR that reports the BIOS setting. > But I don't know which one it is. > > Couldn't you simply over-provision, and then when the CPU is online, use my > ht_enabled statement to figure out whether or not you need to handle the sharing > issue?
I got an idea from Tony,
> If this is worth doing, then perhaps you could write a routine > to check if another HT thread on this same core has already been > brought online ... i.e. defer the allocation to when you see the > second thread. If HT is off, then you'll never see a second thread > so you'll avoid the allocation
We can't defer the allocation to CPU_UP_PREPARE notifier(intel_pmu_cpu_prepare), because the thread cpumask for that booting cpu has not been setup yet.
So below code defers the allocation to CPU_STARTING notifier(intel_pmu_cpu_starting).
static bool ht_enabled(int cpu) { struct cpumask *siblings = topology_thread_cpumask(cpu);
if (!cpu_has(&boot_cpu_data, X86_FEATURE_HT)) return false;
return cpus_weight(*siblings) > 1; }
static void intel_pmu_cpu_starting(int cpu) { struct cpu_hw_events *cpuc = &per_cpu(cpu_hw_events, cpu); struct intel_percore *pc; int core_id = topology_core_id(cpu); int i;
init_debug_store_on_cpu(cpu); /* * Deal with CPUs that don't clear their LBRs on power-up. */ intel_pmu_lbr_reset();
if (!ht_enabled(cpu)) return;
cpuc->per_core = kzalloc_node(sizeof(struct intel_percore), GFP_KERNEL, cpu_to_node(cpu)); if (!cpuc->per_core) return;
raw_spin_lock_init(&cpuc->per_core->lock); pc = cpuc->per_core;
for_each_cpu(i, topology_thread_cpumask(cpu)) { cpuc = &per_cpu(cpu_hw_events, cpu);
cpuc->per_core = pc; cpuc->per_core->core_id = core_id; cpuc->per_core->refcnt++; } }
But when unplug/plug 2 HT threads, I got a BUG.
BUG: sleeping function called from invalid context at /opt/linux-2.6/mm/slub.c:793 in_atomic(): 0, irqs_disabled(): 1, pid: 0, name: kworker/0:1 INFO: lockdep is turned off. irq event stamp: 0 hardirqs last enabled at (0): [< (null)>] (null) hardirqs last disabled at (0): [<ffffffff8106b4f0>] copy_process+0x59d/0x11a7 softirqs last enabled at (0): [<ffffffff8106b4f0>] copy_process+0x59d/0x11a7 softirqs last disabled at (0): [< (null)>] (null) Pid: 0, comm: kworker/0:1 Tainted: G W 2.6.37-rc7-tip-mlin+ #267 Call Trace: [<ffffffff81060144>] ? __might_sleep+0xe9/0xee [<ffffffff81113e14>] ? kmem_cache_alloc_node_notrace+0x49/0xdd [<ffffffff8103f24d>] ? intel_pmu_cpu_starting+0xa8/0x18b [<ffffffff8103f24d>] ? intel_pmu_cpu_starting+0xa8/0x18b [<ffffffff8104669c>] ? generic_set_all+0x25f/0x294 [<ffffffff81735d76>] ? x86_pmu_notifier+0x4b/0x52 [<ffffffff81742e23>] ? notifier_call_chain+0x5e/0x92 [<ffffffff8108cc55>] ? __raw_notifier_call_chain+0x9/0xb [<ffffffff8106e834>] ? __cpu_notify+0x1b/0x2d [<ffffffff8106e854>] ? cpu_notify+0xe/0x10 [<ffffffff81739d43>] ? notify_cpu_starting+0x24/0x26 [<ffffffff817381b4>] ? start_secondary+0x122/0x193
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