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Date: Sun, 01 Apr 2012 11:11:23 +0800
From: "Yan, Zheng" <zheng.z.yan@...el.com>
To: Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC: mingo@...e.hu, andi@...stfloor.org, eranian@...gle.com,
linux-kernel@...r.kernel.org, ming.m.lin@...el.com
Subject: Re: [PATCH 2/5] perf: generic intel uncore support
On 03/31/2012 11:18 AM, Peter Zijlstra wrote:
> On Wed, 2012-03-28 at 14:43 +0800, Yan, Zheng wrote:
>> diff --git a/arch/x86/kernel/cpu/perf_event_intel_uncore.c b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
>> new file mode 100644
>> index 0000000..d159e3e
>> --- /dev/null
>> +++ b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
>> @@ -0,0 +1,814 @@
>> +#include "perf_event_intel_uncore.h"
>> +
>> +static struct intel_uncore_type *empty_uncore[] = { NULL, };
>> +static struct intel_uncore_type **msr_uncores = empty_uncore;
>> +
>> +/* constraint for box with 2 counters */
>> +static struct event_constraint unconstrained_2 =
>> + EVENT_CONSTRAINT(0, 0x3, 0);
>> +/* constraint for box with 3 counters */
>> +static struct event_constraint unconstrained_3 =
>> + EVENT_CONSTRAINT(0, 0x7, 0);
>> +/* constraint for box with 4 counters */
>> +static struct event_constraint unconstrained_4 =
>> + EVENT_CONSTRAINT(0, 0xf, 0);
>> +/* constraint for box with 8 counters */
>> +static struct event_constraint unconstrained_8 =
>> + EVENT_CONSTRAINT(0, 0xff, 0);
>> +/* constraint for the fixed countesr */
>> +static struct event_constraint constraint_fixed =
>> + EVENT_CONSTRAINT((u64)-1, 1 << UNCORE_PMC_IDX_FIXED, (u64)-1);
>
> Since they're all different, why not have an struct event_constraint
> unconstrained member in your struct intel_uncore_pmu and fill it out
> whenever you create that.
>
>> +static DEFINE_SPINLOCK(uncore_box_lock);
>
>> +/*
>> + * The overflow interrupt is unavailable for SandyBridge-EP, is broken
>> + * for SandyBridge. So we use hrtimer to periodically poll the counter
>> + */
>
> To avoid overlow and accumulate into the software u64, right? Not to
> actually sample anything.
Yes
>
> Might also want to say is broken for anything else, since afaik uncore
> PMI has been broken for everything with an uncore.
>
>
>> +static struct intel_uncore_box *
>> +__uncore_pmu_find_box(struct intel_uncore_pmu *pmu, int phyid)
>> +{
>> + struct intel_uncore_box *box;
>> + struct hlist_head *head;
>> + struct hlist_node *node;
>> +
>> + head = &pmu->box_hash[phyid % UNCORE_BOX_HASH_SIZE];
>> +
>> + hlist_for_each_entry_rcu(box, node, head, hlist) {
>> + if (box->phy_id == phyid)
>> + return box;
>> + }
>> +
>> + return NULL;
>> +}
>> +
>> +static struct intel_uncore_box *
>> +uncore_pmu_find_box(struct intel_uncore_pmu *pmu, int phyid)
>> +{
>> + struct intel_uncore_box *box;
>> +
>> + rcu_read_lock();
>> + box = __uncore_pmu_find_box(pmu, phyid);
>> + rcu_read_unlock();
>> +
>> + return box;
>> +}
>> +
>> +/* caller should hold the uncore_box_lock */
>> +static void uncore_pmu_add_box(struct intel_uncore_pmu *pmu,
>> + struct intel_uncore_box *box)
>> +{
>> + struct hlist_head *head;
>> +
>> + head = &pmu->box_hash[box->phy_id % UNCORE_BOX_HASH_SIZE];
>> + hlist_add_head_rcu(&box->hlist, head);
>> +}
>> +
>> +static struct intel_uncore_pmu *uncore_event_to_pmu(struct perf_event *event)
>> +{
>> + return container_of(event->pmu, struct intel_uncore_pmu, pmu);
>> +}
>> +
>> +static struct intel_uncore_box *uncore_event_to_box(struct perf_event *event)
>> +{
>> + int phyid = topology_physical_package_id(smp_processor_id());
>
> Who says that this event has anything to do with the current cpu?
>
Because perf core schedules event on the basis of cpu.
>> + return uncore_pmu_find_box(uncore_event_to_pmu(event), phyid);
>> +}
>
> So why not simply use a per-cpu allocation and have something like:
>
> struct intel_uncore_pmu {
> ...
> struct intel_uncore_box * __percpu box;
> };
>
> static inline
> struct intel_uncore_box *uncore_event_to_box(struct perf_event *event)
> {
> return per_cpu_ptr(event->pmu->box, event->cpu);
> }
>
> And be done with it?
Because using per-cpu allocation is inconvenience for PCI uncore device.
>
>> +static int uncore_collect_events(struct intel_uncore_box *box,
>> + struct perf_event *leader, bool dogrp)
>> +{
>> + struct perf_event *event;
>> + int n, max_count;
>> +
>> + max_count = box->pmu->type->num_counters;
>> + if (box->pmu->type->fixed_ctl)
>> + max_count++;
>> +
>> + if (box->n_events >= max_count)
>> + return -EINVAL;
>> +
>> + /*
>> + * adding the same events twice to the uncore PMU may cause
>> + * general protection fault
>> + */
>
> Is that an errata or a 'feature' of some specific box types, or what?
>
>> + for (n = 0; n < box->n_events; n++) {
>> + event = box->event_list[n];
>> + if (event->hw.config == leader->hw.config)
>> + return -EINVAL;
>> + }
>> +
>> + n = box->n_events;
>> + box->event_list[n] = leader;
>> + n++;
>> + if (!dogrp)
>> + return n;
>> +
>> + list_for_each_entry(event, &leader->sibling_list, group_entry) {
>> + if (event->state <= PERF_EVENT_STATE_OFF)
>> + continue;
>> +
>> + if (n >= max_count)
>> + return -EINVAL;
>> +
>> + box->event_list[n] = event;
>> + n++;
>> + }
>> + return n;
>> +}
>> +
>> +static struct event_constraint *
>> +uncore_event_constraint(struct intel_uncore_type *type,
>> + struct perf_event *event)
>> +{
>> + struct event_constraint *c;
>> +
>> + if (event->hw.config == (u64)-1)
>> + return &constraint_fixed;
>> +
>> + if (type->constraints) {
>> + for_each_event_constraint(c, type->constraints) {
>> + if ((event->hw.config & c->cmask) == c->code)
>> + return c;
>> + }
>> + }
>> +
>> + if (type->num_counters == 2)
>> + return &unconstrained_2;
>> + if (type->num_counters == 3)
>> + return &unconstrained_3;
>> + if (type->num_counters == 4)
>> + return &unconstrained_4;
>> + if (type->num_counters == 8)
>> + return &unconstrained_8;
>> +
>> + WARN_ON_ONCE(1);
>> + return &unconstrained_2;
>
> return event->pmu->unconstrained;
>
> seems much saner to me..
will change the code
>
>> +}
>> +
>> +static int uncore_assign_events(struct intel_uncore_box *box,
>> + int assign[], int n)
>> +{
>> + struct event_constraint *c, *constraints[UNCORE_PMC_IDX_MAX];
>> + int i, ret, wmin, wmax;
>> +
>> + for (i = 0, wmin = X86_PMC_IDX_MAX, wmax = 0; i < n; i++) {
>> + c = uncore_event_constraint(box->pmu->type,
>> + box->event_list[i]);
>> + constraints[i] = c;
>> + wmin = min(wmin, c->weight);
>> + wmax = max(wmax, c->weight);
>> + }
>
> No fast path then?
will add the fast path
>
>> + ret = perf_assign_events(constraints, n, wmin, wmax, assign);
>> + return ret ? -EINVAL : 0;
>> +}
>
>
>> +static void uncore_pmu_event_start(struct perf_event *event, int flags)
>> +{
>> + struct intel_uncore_box *box = uncore_event_to_box(event);
>> +
>> + raw_spin_lock(&box->lock);
>> + __uncore_pmu_event_start(box, event, flags);
>> + raw_spin_unlock(&box->lock);
>> +}
>
>> +static void uncore_pmu_event_stop(struct perf_event *event, int flags)
>> +{
>> + struct intel_uncore_box *box = uncore_event_to_box(event);
>> +
>> + raw_spin_lock(&box->lock);
>> + __uncore_pmu_event_stop(box, event, flags);
>> + raw_spin_unlock(&box->lock);
>> +}
>
>> +static int uncore_pmu_event_add(struct perf_event *event, int flags)
>> +{
>> + struct intel_uncore_box *box = uncore_event_to_box(event);
>> + struct hw_perf_event *hwc = &event->hw;
>> + int assign[UNCORE_PMC_IDX_MAX];
>> + int i, n, ret;
>> +
>> + if (!box)
>> + return -ENODEV;
>> +
>> + raw_spin_lock(&box->lock);
>
>> + raw_spin_unlock(&box->lock);
>> + return ret;
>> +}
>> +
>> +static void uncore_pmu_event_del(struct perf_event *event, int flags)
>> +{
>> + struct intel_uncore_box *box = uncore_event_to_box(event);
>> + int i;
>> +
>> + raw_spin_lock(&box->lock);
>
>> + raw_spin_unlock(&box->lock);
>> +}
>
> So what's up with all this box->lock business.. why does that lock
> exist?
If user doesn't provide the "-C x" option to the perf tool, multiple cpus
will try adding/deleting events at the same time.
>
>> +static int __init uncore_pmu_register(struct intel_uncore_pmu *pmu)
>> +{
>> + int ret;
>> +
>> + pmu->pmu.attr_groups = pmu->type->attr_groups;
>> + pmu->pmu.task_ctx_nr = perf_invalid_context;
>> + pmu->pmu.event_init = uncore_pmu_event_init;
>> + pmu->pmu.add = uncore_pmu_event_add;
>> + pmu->pmu.del = uncore_pmu_event_del;
>> + pmu->pmu.start = uncore_pmu_event_start;
>> + pmu->pmu.stop = uncore_pmu_event_stop;
>> + pmu->pmu.read = uncore_pmu_event_read;
>
> Won't this look better as a C99 struct init? Something like:
>
> pmu->pmu = (struct pmu){
> .attr_groups = pmu->type->attr_groups,
> .task_ctx_nr = perf_invalid_context,
> .event_init = uncore_pmu_event_init,
> ...
> };
>
>> + if (pmu->type->num_boxes == 1)
>> + sprintf(pmu->name, "uncore_%s", pmu->type->name);
>> + else
>> + sprintf(pmu->name, "uncore_%s%d", pmu->type->name,
>> + pmu->pmu_idx);
>> +
>> + ret = perf_pmu_register(&pmu->pmu, pmu->name, -1);
>> + return ret;
>> +}
>
>
>> +static int __init uncore_type_init(struct intel_uncore_type *type)
>> +{
>> + struct intel_uncore_pmu *pmus;
>> + struct attribute_group *events_group;
>> + struct attribute **attrs;
>> + int i, j;
>> +
>> + pmus = kzalloc(sizeof(*pmus) * type->num_boxes, GFP_KERNEL);
>> + if (!pmus)
>> + return -ENOMEM;
>
> Hmm, but if you have a pmu per number of boxes, then what do you need
> that pmu->box reference for?
Type->num_boxes is number of boxes within one physical cpu. pmu->box_hash
is needed because there can be several physical cpus in a system.
>
>> +
>> + for (i = 0; i < type->num_boxes; i++) {
>> + pmus[i].func_id = -1;
>> + pmus[i].pmu_idx = i;
>> + pmus[i].type = type;
>> +
>> + for (j = 0; j < ARRAY_SIZE(pmus[0].box_hash); j++)
>> + INIT_HLIST_HEAD(&pmus[i].box_hash[j]);
>> + }
>> +
>> + if (type->event_descs) {
>> + for (i = 0; ; i++) {
>> + if (!type->event_descs[i].attr.attr.name)
>> + break;
>> + }
>> +
>> + events_group = kzalloc(sizeof(struct attribute *) * (i + 1) +
>> + sizeof(*events_group), GFP_KERNEL);
>> + if (!events_group)
>> + goto fail;
>> +
>> + attrs = (struct attribute **)(events_group + 1);
>> + events_group->name = "events";
>> + events_group->attrs = attrs;
>> +
>> + for (j = 0; j < i; j++)
>> + attrs[j] = &type->event_descs[j].attr.attr;
>> +
>> + type->attr_groups[1] = events_group;
>> + }
>> + type->pmus = pmus;
>> + return 0;
>> +fail:
>> + uncore_type_exit(type);
>> + return -ENOMEM;
>> +}
>> +
>
>
> Aside from all this, there's still the problem that you don't place all
> events for a particular phys_id onto a single cpu. It doesn't matter
> which cpu in that package it is, but all events should go to the same.
>
> This means that on unplug of that cpu, you have to migrate all these
> events etc..
Any hints how to do this. I'm afraid it requires big changes to perf core.
Thank you very much
Yan, Zheng
>
> I suspect doing this will also allow you to get rid of that box->lock
> thing.
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