Messages in this thread |  | | | Subject | Re: [PATCH] perf/x86: check ucode before disabling PEBS on SandyBridge | | From | Peter Zijlstra <> | | Date | Fri, 08 Jun 2012 16:45:18 +0200 |
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On Fri, 2012-06-08 at 16:36 +0200, Borislav Petkov wrote: > On Fri, Jun 08, 2012 at 04:20:50PM +0200, Peter Zijlstra wrote: > > On Fri, 2012-06-08 at 16:15 +0200, Borislav Petkov wrote: > > > have a variable which gets initialized to the number of all CPUs and > > > each time ->apply_microcode() finishes by returning 0, we decrement it > > > once. > > > > > > > > Hmm, I'm probably missing some obscure case. > > > > Since its all per-cpu sysfs muck, userspace could update a random > > subsets of cpus.. leaving us hanging. > > I'm afraid I don't understand - when you modprobe microcode.ko, > it goes and loads /lib/firmware/amd-ucode/microcode_amd.bin (in > the AMD case) on each CPU when the driver gets regged through > subsys_interface_register(). > > It calls ->add_dev() on each CPU - this should be guaranteed because it > uses the cpu_subsys from drivers/base/cpu.c which onlines all CPUs, I'd > assume. > > So, I'd say that once subsys_interface_register() returns, we have > updated ucode on all CPUs, if successful... > > We probably could run the notifier at that moment, before we do > put_online_cpus().
I was thinking about reload_store(), that seems to only reload ucode for a single cpu.
> > The 'bestestet' idea I came up with is doing the verify thing I have > > from a delayed work -- say 1 second into the future. That way, when > > there's lots of cpus they all try and enqueue the one work, which at > > the end executes only once, provided the entire update scan took less > > than the second. > > You're saying, you want the last CPU that gets to update its microcode > gets to also run the delayed work...? Probably, I'd assume ucode update > on a single CPU takes less than a second IIUC.
Nah.. it'll probably be the first. But it doesn't matter which cpu does it. So the idea was:
static void intel_snb_verify_work(struct work_struct *work) { /* do the verify thing.. */ } static DECLARE_DELAYED_WORK(intel_snb_delayed_work, intel_snb_verify_ucode);
static int intel_snb_ucode_notifier(struct notifier_block *self, unsigned long action, void *_uci) { /* * Since ucode cannot be down-graded, and no future ucode revision * is known to break PEBS again, we're ok with MICROCODE_CAN_UPDATE. */ if (action == MICROCODE_UPDATED) schedule_delayed_work(&intel_snb_delayed_work, HZ); return NOTIFY_DONE; } Thus it will queue the delayed work when the work isn't already queued for execution. Resulting in the work only happening once a second (at most).
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