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RE: [PATCH V5] perf/x86: add sysfs entry to freeze counter on SMI

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  RE: [PATCH V5] perf/x86: add sysfs entry to freeze counter on SMI "Liang, Kan" <kan.liang@intel.com> - 2017-05-08 15:40 +0200
    RE: [PATCH V5] perf/x86: add sysfs entry to freeze counter on SMI Thomas Gleixner <tglx@linutronix.de> - 2017-05-10 16:00 +0200
      RE: [PATCH V5] perf/x86: add sysfs entry to freeze counter on SMI "Liang, Kan" <kan.liang@intel.com> - 2017-05-10 17:50 +0200

#1637449 — RE: [PATCH V5] perf/x86: add sysfs entry to freeze counter on SMI

Hi tglx,

Are you OK with patch?
Could I get your "acked-by"?

Thanks,
Kan
> 
> 
> Ping.
> Any comments for the patch?
> 
> Thanks,
> Kan
> 
> > Subject: [PATCH V5] perf/x86: add sysfs entry to freeze counter on SMI
> >
> > From: Kan Liang <Kan.liang@intel.com>
> >
> > Currently, the SMIs are visible to all performance counters. Because
> > many users want to measure everything including SMIs. But in some
> > cases, the SMI cycles should not be count. For example, to calculate
> > the cost of SMI itself. So a knob is needed.
> >
> > When setting FREEZE_WHILE_SMM bit in IA32_DEBUGCTL, all performance
> > counters will be effected. There is no way to do per-counter freeze on SMI.
> > So it should not use the per-event interface (e.g. ioctl or event
> > attribute) to set FREEZE_WHILE_SMM bit.
> >
> > Adds sysfs entry /sys/device/cpu/freeze_on_smi to set
> FREEZE_WHILE_SMM
> > bit in IA32_DEBUGCTL. When set, freezes perfmon and trace messages
> > while in SMM.
> > Value has to be 0 or 1. It will be applied to all processors.
> > Also serialize the entire setting so we don't get multiple concurrent
> > threads trying to update to different values.
> >
> > Signed-off-by: Kan Liang <Kan.liang@intel.com>
> > ---
> >
> > Changes since V4:
> >  - drop msr_flip_bit function
> >  - Use on_each_cpu() which already include all the needed protection
> >  - Some small changes according to the comments
> >
> >  arch/x86/events/core.c           | 10 +++++++
> >  arch/x86/events/intel/core.c     | 63
> > ++++++++++++++++++++++++++++++++++++++++
> >  arch/x86/events/perf_event.h     |  3 ++
> >  arch/x86/include/asm/msr-index.h |  2 ++
> >  4 files changed, 78 insertions(+)
> >
> > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index
> > 349d4d1..c16fb50 100644
> > --- a/arch/x86/events/core.c
> > +++ b/arch/x86/events/core.c
> > @@ -1750,6 +1750,8 @@ ssize_t x86_event_sysfs_show(char *page, u64
> > config, u64 event)
> >  	return ret;
> >  }
> >
> > +static struct attribute_group x86_pmu_attr_group;
> > +
> >  static int __init init_hw_perf_events(void)  {
> >  	struct x86_pmu_quirk *quirk;
> > @@ -1813,6 +1815,14 @@ static int __init init_hw_perf_events(void)
> >  			x86_pmu_events_group.attrs = tmp;
> >  	}
> >
> > +	if (x86_pmu.attrs) {
> > +		struct attribute **tmp;
> > +
> > +		tmp = merge_attr(x86_pmu_attr_group.attrs, x86_pmu.attrs);
> > +		if (!WARN_ON(!tmp))
> > +			x86_pmu_attr_group.attrs = tmp;
> > +	}
> > +
> >  	pr_info("... version:                %d\n",     x86_pmu.version);
> >  	pr_info("... bit width:              %d\n",     x86_pmu.cntval_bits);
> >  	pr_info("... generic registers:      %d\n",     x86_pmu.num_counters);
> > diff --git a/arch/x86/events/intel/core.c
> > b/arch/x86/events/intel/core.c index
> > 4244bed..a5bc4e4 100644
> > --- a/arch/x86/events/intel/core.c
> > +++ b/arch/x86/events/intel/core.c
> > @@ -3160,6 +3160,19 @@ static int intel_pmu_cpu_prepare(int cpu)
> >  	return -ENOMEM;
> >  }
> >
> > +static void flip_smm_bit(void *data)
> > +{
> > +	bool set = *(int *)data;
> > +
> > +	if (set) {
> > +		msr_set_bit(MSR_IA32_DEBUGCTLMSR,
> > +			    DEBUGCTLMSR_FREEZE_IN_SMM_BIT);
> > +	} else {
> > +		msr_clear_bit(MSR_IA32_DEBUGCTLMSR,
> > +			      DEBUGCTLMSR_FREEZE_IN_SMM_BIT);
> > +	}
> > +}
> > +
> >  static void intel_pmu_cpu_starting(int cpu)  {
> >  	struct cpu_hw_events *cpuc = &per_cpu(cpu_hw_events, cpu); @@ -
> > 3174,6 +3187,8 @@ static void intel_pmu_cpu_starting(int cpu)
> >
> >  	cpuc->lbr_sel = NULL;
> >
> > +	flip_smm_bit(&x86_pmu.attr_freeze_on_smi);
> > +
> >  	if (!cpuc->shared_regs)
> >  		return;
> >
> > @@ -3595,6 +3610,52 @@ static struct attribute *hsw_events_attrs[] = {
> >  	NULL
> >  };
> >
> > +static ssize_t freeze_on_smi_show(struct device *cdev,
> > +				  struct device_attribute *attr,
> > +				  char *buf)
> > +{
> > +	return sprintf(buf, "%d\n", x86_pmu.attr_freeze_on_smi); }
> > +
> > +static DEFINE_MUTEX(freeze_on_smi_mutex);
> > +
> > +static ssize_t freeze_on_smi_store(struct device *cdev,
> > +				   struct device_attribute *attr,
> > +				   const char *buf, size_t count) {
> > +	unsigned long val;
> > +	ssize_t ret;
> > +
> > +	ret = kstrtoul(buf, 0, &val);
> > +	if (ret)
> > +		return ret;
> > +
> > +	if (val > 1)
> > +		return -EINVAL;
> > +
> > +	mutex_lock(&freeze_on_smi_mutex);
> > +
> > +	if (x86_pmu.attr_freeze_on_smi == val)
> > +		goto done;
> > +
> > +	x86_pmu.attr_freeze_on_smi = val;
> > +
> > +	get_online_cpus();
> > +	on_each_cpu(flip_smm_bit, &val, 1);
> > +	put_online_cpus();
> > +done:
> > +	mutex_unlock(&freeze_on_smi_mutex);
> > +
> > +	return count;
> > +}
> > +
> > +static DEVICE_ATTR_RW(freeze_on_smi);
> > +
> > +static struct attribute *intel_pmu_attrs[] = {
> > +	&dev_attr_freeze_on_smi.attr,
> > +	NULL,
> > +};
> > +
> >  __init int intel_pmu_init(void)
> >  {
> >  	union cpuid10_edx edx;
> > @@ -3641,6 +3702,8 @@ __init int intel_pmu_init(void)
> >
> >  	x86_pmu.max_pebs_events		= min_t(unsigned,
> > MAX_PEBS_EVENTS, x86_pmu.num_counters);
> >
> > +
> > +	x86_pmu.attrs			= intel_pmu_attrs;
> >  	/*
> >  	 * Quirk: v2 perfmon does not report fixed-purpose events, so
> >  	 * assume at least 3 events, when not running in a hypervisor:
> > diff --git a/arch/x86/events/perf_event.h
> > b/arch/x86/events/perf_event.h index bcbb1d2..110cb9b0 100644
> > --- a/arch/x86/events/perf_event.h
> > +++ b/arch/x86/events/perf_event.h
> > @@ -561,6 +561,9 @@ struct x86_pmu {
> >  	ssize_t		(*events_sysfs_show)(char *page, u64 config);
> >  	struct attribute **cpu_events;
> >
> > +	int		attr_freeze_on_smi;
> > +	struct attribute **attrs;
> > +
> >  	/*
> >  	 * CPU Hotplug hooks
> >  	 */
> > diff --git a/arch/x86/include/asm/msr-index.h
> > b/arch/x86/include/asm/msr- index.h index d8b5f8a..0572f91 100644
> > --- a/arch/x86/include/asm/msr-index.h
> > +++ b/arch/x86/include/asm/msr-index.h
> > @@ -134,6 +134,8 @@
> >  #define DEBUGCTLMSR_BTS_OFF_OS		(1UL <<  9)
> >  #define DEBUGCTLMSR_BTS_OFF_USR		(1UL << 10)
> >  #define DEBUGCTLMSR_FREEZE_LBRS_ON_PMI	(1UL << 11)
> > +#define DEBUGCTLMSR_FREEZE_IN_SMM_BIT	14
> > +#define DEBUGCTLMSR_FREEZE_IN_SMM	(1UL <<
> > DEBUGCTLMSR_FREEZE_IN_SMM_BIT)
> >
> >  #define MSR_PEBS_FRONTEND		0x000003f7
> >
> > --
> > 2.7.4

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#1638859

On Mon, 8 May 2017, Liang, Kan wrote:

> Hi tglx,
> 
> Are you OK with patch?
> Could I get your "acked-by"?

No.

> > > +static void flip_smm_bit(void *data)
> > > +{
> > > +	bool set = *(int *)data;

data points to an unsigned long. So while this works on LE machines this is
still crap.

> > > +	if (set) {
> > > +		msr_set_bit(MSR_IA32_DEBUGCTLMSR,
> > > +			    DEBUGCTLMSR_FREEZE_IN_SMM_BIT);
> > > +	} else {
> > > +		msr_clear_bit(MSR_IA32_DEBUGCTLMSR,
> > > +			      DEBUGCTLMSR_FREEZE_IN_SMM_BIT);
> > > +	}

I probably forgot, but why do we need an open coded version of __flip_bit()
instead of reusing that?

Thanks,

	tglx

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#1638921

> 
> > > > +static void flip_smm_bit(void *data) {
> > > > +	bool set = *(int *)data;
> 
> data points to an unsigned long. So while this works on LE machines this is
> still crap.

I will change the code as below.
+static void flip_smm_bit(void *data)
+{
+       unsigned long set = *(unsigned long *)data;
+
+       if (set > 0) {

> 
> > > > +	if (set) {
> > > > +		msr_set_bit(MSR_IA32_DEBUGCTLMSR,
> > > > +			    DEBUGCTLMSR_FREEZE_IN_SMM_BIT);
> > > > +	} else {
> > > > +		msr_clear_bit(MSR_IA32_DEBUGCTLMSR,
> > > > +			      DEBUGCTLMSR_FREEZE_IN_SMM_BIT);
> > > > +	}
> 
> I probably forgot, but why do we need an open coded version of __flip_bit()
> instead of reusing that?
> 
msr_set_bit/msr_clear_bit is enough for our requirement. There is no extra
work needed.
__flip_bit is static inline. If we want to directly use it, we have to expose
it by an additional patch. If so, we will have two sets of interfaces to flip MSR
bit. I think it's too much.
What do you think?

Thanks,
Kan

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