[PATCH 7/9] powerpc/perf: Core EBB support for 64-bit book3s
Michael Ellerman
michael at ellerman.id.au
Fri Jun 28 18:15:16 EST 2013
Add support for EBB (Event Based Branches) on 64-bit book3s. See the
included documentation for more details.
EBBs are a feature which allows the hardware to branch directly to a
specified user space address when a PMU event overflows. This can be
used by programs for self-monitoring with no kernel involvement in the
inner loop.
Most of the logic is in the generic book3s code, primarily to avoid a
proliferation of PMU callbacks.
Signed-off-by: Michael Ellerman <michael at ellerman.id.au>
---
v2: Flesh out the documentation further.
---
Documentation/powerpc/00-INDEX | 2 +
Documentation/powerpc/pmu-ebb.txt | 137 ++++++++++++++++++++++
arch/powerpc/include/asm/perf_event_server.h | 6 +
arch/powerpc/include/asm/processor.h | 3 +-
arch/powerpc/include/asm/reg.h | 8 ++
arch/powerpc/include/asm/switch_to.h | 14 +++
arch/powerpc/kernel/process.c | 4 +
arch/powerpc/perf/core-book3s.c | 161 +++++++++++++++++++++++---
8 files changed, 321 insertions(+), 14 deletions(-)
create mode 100644 Documentation/powerpc/pmu-ebb.txt
diff --git a/Documentation/powerpc/00-INDEX b/Documentation/powerpc/00-INDEX
index dd9e928..05026ce 100644
--- a/Documentation/powerpc/00-INDEX
+++ b/Documentation/powerpc/00-INDEX
@@ -14,6 +14,8 @@ hvcs.txt
- IBM "Hypervisor Virtual Console Server" Installation Guide
mpc52xx.txt
- Linux 2.6.x on MPC52xx family
+pmu-ebb.txt
+ - Description of the API for using the PMU with Event Based Branches.
qe_firmware.txt
- describes the layout of firmware binaries for the Freescale QUICC
Engine and the code that parses and uploads the microcode therein.
diff --git a/Documentation/powerpc/pmu-ebb.txt b/Documentation/powerpc/pmu-ebb.txt
new file mode 100644
index 0000000..73cd163
--- /dev/null
+++ b/Documentation/powerpc/pmu-ebb.txt
@@ -0,0 +1,137 @@
+PMU Event Based Branches
+========================
+
+Event Based Branches (EBBs) are a feature which allows the hardware to
+branch directly to a specified user space address when certain events occur.
+
+The full specification is available in Power ISA v2.07:
+
+ https://www.power.org/documentation/power-isa-version-2-07/
+
+One type of event for which EBBs can be configured is PMU exceptions. This
+document describes the API for configuring the Power PMU to generate EBBs,
+using the Linux perf_events API.
+
+
+Terminology
+-----------
+
+Throughout this document we will refer to an "EBB event" or "EBB events". This
+just refers to a struct perf_event which has set the "EBB" flag in its
+attr.config. All events which can be configured on the hardware PMU are
+possible "EBB events".
+
+
+Background
+----------
+
+When a PMU EBB occurs it is delivered to the currently running process. As such
+EBBs can only sensibly be used by programs for self-monitoring.
+
+It is a feature of the perf_events API that events can be created on other
+processes, subject to standard permission checks. This is also true of EBB
+events, however unless the target process enables EBBs (via mtspr(BESCR)) no
+EBBs will ever be delivered.
+
+This makes it possible for a process to enable EBBs for itself, but not
+actually configure any events. At a later time another process can come along
+and attach an EBB event to the process, which will then cause EBBs to be
+delivered to the first process. It's not clear if this is actually useful.
+
+
+When the PMU is configured for EBBs, all PMU interrupts are delivered to the
+user process. This means once an EBB event is scheduled on the PMU, no non-EBB
+events can be configured. This means that EBB events can not be run
+concurrently with regular 'perf' commands, or any other perf events.
+
+It is however safe to run 'perf' commands on a process which is using EBBs. The
+kernel will in general schedule the EBB event, and perf will be notified that
+its events could not run.
+
+The exclusion between EBB events and regular events is implemented using the
+existing "pinned" and "exclusive" attributes of perf_events. This means EBB
+events will be given priority over other events, unless they are also pinned.
+If an EBB event and a regular event are both pinned, then whichever is enabled
+first will be scheduled and the other will be put in error state. See the
+section below titled "Enabling an EBB event" for more information.
+
+
+Creating an EBB event
+---------------------
+
+To request that an event is counted using EBB, the event code should have bit
+63 set.
+
+EBB events must be created with a particular, and restrictive, set of
+attributes - this is so that they interoperate correctly with the rest of the
+perf_events subsystem.
+
+An EBB event must be created with the "pinned" and "exclusive" attributes set.
+Note that if you are creating a group of EBB events, only the leader can have
+these attributes set.
+
+An EBB event must NOT set any of the "inherit", "sample_period", "freq" or
+"enable_on_exec" attributes.
+
+An EBB event must be attached to a task. This is specified to perf_event_open()
+by passing a pid value, typically 0 indicating the current task.
+
+All events in a group must agree on whether they want EBB. That is all events
+must request EBB, or none may request EBB.
+
+EBB events must specify the PMC they are to be counted on. This ensures
+userspace is able to reliably determine which PMC the event is scheduled on.
+
+
+Enabling an EBB event
+---------------------
+
+Once an EBB event has been successfully opened, it must be enabled with the
+perf_events API. This can be achieved either via the ioctl() interface, or the
+prctl() interface.
+
+However, due to the design of the perf_events API, enabling an event does not
+guarantee that it has been scheduled on the PMU. To ensure that the EBB event
+has been scheduled on the PMU, you must perform a read() on the event. If the
+read() returns EOF, then the event has not been scheduled and EBBs are not
+enabled.
+
+This behaviour occurs because the EBB event is pinned and exclusive. When the
+EBB event is enabled it will force all other non-pinned events off the PMU. In
+this case the enable will be successful. However if there is already an event
+pinned on the PMU then the enable will not be successful.
+
+
+Reading an EBB event
+--------------------
+
+It is possible to read() from an EBB event. However the results are
+meaningless. Because interrupts are being delivered to the user process the
+kernel is not able to count the event, and so will return a junk value.
+
+
+Closing an EBB event
+--------------------
+
+When an EBB event is finished with, you can close it using close() as for any
+regular event. If this is the last EBB event the PMU will be deconfigured and
+no further PMU EBBs will be delivered.
+
+
+EBB Handler
+-----------
+
+The EBB handler is just regular userspace code, however it must be written in
+the style of an interrupt handler. When the handler is entered all registers
+are live (possibly) and so must be saved somehow before the handler can invoke
+other code.
+
+It's up to the program how to handle this. For C programs a relatively simple
+option is to create an interrupt frame on the stack and save registers there.
+
+Fork
+----
+
+EBB events are not inherited across fork. If the child process wishes to use
+EBBs it should open a new event for itself. Similarly the EBB state in
+BESCR/EBBHR/EBBRR is cleared across fork().
diff --git a/arch/powerpc/include/asm/perf_event_server.h b/arch/powerpc/include/asm/perf_event_server.h
index f265049..2dd7bfc 100644
--- a/arch/powerpc/include/asm/perf_event_server.h
+++ b/arch/powerpc/include/asm/perf_event_server.h
@@ -60,6 +60,7 @@ struct power_pmu {
#define PPMU_HAS_SSLOT 0x00000020 /* Has sampled slot in MMCRA */
#define PPMU_HAS_SIER 0x00000040 /* Has SIER */
#define PPMU_BHRB 0x00000080 /* has BHRB feature enabled */
+#define PPMU_EBB 0x00000100 /* supports event based branch */
/*
* Values for flags to get_alternatives()
@@ -68,6 +69,11 @@ struct power_pmu {
#define PPMU_LIMITED_PMC_REQD 2 /* have to put this on a limited PMC */
#define PPMU_ONLY_COUNT_RUN 4 /* only counting in run state */
+/*
+ * We use the event config bit 63 as a flag to request EBB.
+ */
+#define EVENT_CONFIG_EBB_SHIFT 63
+
extern int register_power_pmu(struct power_pmu *);
struct pt_regs;
diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index 3f19df3..47a35b0 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -287,8 +287,9 @@ struct thread_struct {
unsigned long siar;
unsigned long sdar;
unsigned long sier;
- unsigned long mmcr0;
unsigned long mmcr2;
+ unsigned mmcr0;
+ unsigned used_ebb;
#endif
};
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 362142b..5d7d9c2 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -621,6 +621,9 @@
#define MMCR0_PMXE 0x04000000UL /* performance monitor exception enable */
#define MMCR0_FCECE 0x02000000UL /* freeze ctrs on enabled cond or event */
#define MMCR0_TBEE 0x00400000UL /* time base exception enable */
+#define MMCR0_EBE 0x00100000UL /* Event based branch enable */
+#define MMCR0_PMCC 0x000c0000UL /* PMC control */
+#define MMCR0_PMCC_U6 0x00080000UL /* PMC1-6 are R/W by user (PR) */
#define MMCR0_PMC1CE 0x00008000UL /* PMC1 count enable*/
#define MMCR0_PMCjCE 0x00004000UL /* PMCj count enable*/
#define MMCR0_TRIGGER 0x00002000UL /* TRIGGER enable */
@@ -674,6 +677,11 @@
#define SIER_SIAR_VALID 0x0400000 /* SIAR contents valid */
#define SIER_SDAR_VALID 0x0200000 /* SDAR contents valid */
+/* When EBB is enabled, some of MMCR0/MMCR2/SIER are user accessible */
+#define MMCR0_USER_MASK (MMCR0_FC | MMCR0_PMXE | MMCR0_PMAO)
+#define MMCR2_USER_MASK 0x4020100804020000UL /* (FC1P|FC2P|FC3P|FC4P|FC5P|FC6P) */
+#define SIER_USER_MASK 0x7fffffUL
+
#define SPRN_PA6T_MMCR0 795
#define PA6T_MMCR0_EN0 0x0000000000000001UL
#define PA6T_MMCR0_EN1 0x0000000000000002UL
diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h
index 200d763..49a13e0 100644
--- a/arch/powerpc/include/asm/switch_to.h
+++ b/arch/powerpc/include/asm/switch_to.h
@@ -67,4 +67,18 @@ static inline void flush_spe_to_thread(struct task_struct *t)
}
#endif
+static inline void clear_task_ebb(struct task_struct *t)
+{
+#ifdef CONFIG_PPC_BOOK3S_64
+ /* EBB perf events are not inherited, so clear all EBB state. */
+ t->thread.bescr = 0;
+ t->thread.mmcr2 = 0;
+ t->thread.mmcr0 = 0;
+ t->thread.siar = 0;
+ t->thread.sdar = 0;
+ t->thread.sier = 0;
+ t->thread.used_ebb = 0;
+#endif
+}
+
#endif /* _ASM_POWERPC_SWITCH_TO_H */
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index b0f3e3f..f8a76e6 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -916,7 +916,11 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
flush_altivec_to_thread(src);
flush_vsx_to_thread(src);
flush_spe_to_thread(src);
+
*dst = *src;
+
+ clear_task_ebb(dst);
+
return 0;
}
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index d3ee2e5..c6bbbf9 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -77,6 +77,9 @@ static unsigned int freeze_events_kernel = MMCR0_FCS;
#define MMCR0_PMCjCE MMCR0_PMCnCE
#define MMCR0_FC56 0
#define MMCR0_PMAO 0
+#define MMCR0_EBE 0
+#define MMCR0_PMCC 0
+#define MMCR0_PMCC_U6 0
#define SPRN_MMCRA SPRN_MMCR2
#define MMCRA_SAMPLE_ENABLE 0
@@ -104,6 +107,15 @@ static inline int siar_valid(struct pt_regs *regs)
return 1;
}
+static bool is_ebb_event(struct perf_event *event) { return false; }
+static int ebb_event_check(struct perf_event *event) { return 0; }
+static void ebb_event_add(struct perf_event *event) { }
+static void ebb_switch_out(unsigned long mmcr0) { }
+static unsigned long ebb_switch_in(bool ebb, unsigned long mmcr0)
+{
+ return mmcr0;
+}
+
static inline void power_pmu_bhrb_enable(struct perf_event *event) {}
static inline void power_pmu_bhrb_disable(struct perf_event *event) {}
void power_pmu_flush_branch_stack(void) {}
@@ -464,6 +476,89 @@ void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw)
return;
}
+static bool is_ebb_event(struct perf_event *event)
+{
+ /*
+ * This could be a per-PMU callback, but we'd rather avoid the cost. We
+ * check that the PMU supports EBB, meaning those that don't can still
+ * use bit 63 of the event code for something else if they wish.
+ */
+ return (ppmu->flags & PPMU_EBB) &&
+ ((event->attr.config >> EVENT_CONFIG_EBB_SHIFT) & 1);
+}
+
+static int ebb_event_check(struct perf_event *event)
+{
+ struct perf_event *leader = event->group_leader;
+
+ /* Event and group leader must agree on EBB */
+ if (is_ebb_event(leader) != is_ebb_event(event))
+ return -EINVAL;
+
+ if (is_ebb_event(event)) {
+ if (!(event->attach_state & PERF_ATTACH_TASK))
+ return -EINVAL;
+
+ if (!leader->attr.pinned || !leader->attr.exclusive)
+ return -EINVAL;
+
+ if (event->attr.inherit || event->attr.sample_period ||
+ event->attr.enable_on_exec || event->attr.freq)
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+static void ebb_event_add(struct perf_event *event)
+{
+ if (!is_ebb_event(event) || current->thread.used_ebb)
+ return;
+
+ /*
+ * IFF this is the first time we've added an EBB event, set
+ * PMXE in the user MMCR0 so we can detect when it's cleared by
+ * userspace. We need this so that we can context switch while
+ * userspace is in the EBB handler (where PMXE is 0).
+ */
+ current->thread.used_ebb = 1;
+ current->thread.mmcr0 |= MMCR0_PMXE;
+}
+
+static void ebb_switch_out(unsigned long mmcr0)
+{
+ if (!(mmcr0 & MMCR0_EBE))
+ return;
+
+ current->thread.siar = mfspr(SPRN_SIAR);
+ current->thread.sier = mfspr(SPRN_SIER);
+ current->thread.sdar = mfspr(SPRN_SDAR);
+ current->thread.mmcr0 = mmcr0 & MMCR0_USER_MASK;
+ current->thread.mmcr2 = mfspr(SPRN_MMCR2) & MMCR2_USER_MASK;
+}
+
+static unsigned long ebb_switch_in(bool ebb, unsigned long mmcr0)
+{
+ if (!ebb)
+ goto out;
+
+ /* Enable EBB and read/write to all 6 PMCs for userspace */
+ mmcr0 |= MMCR0_EBE | MMCR0_PMCC_U6;
+
+ /* Add any bits from the user reg, FC or PMAO */
+ mmcr0 |= current->thread.mmcr0;
+
+ /* Be careful not to set PMXE if userspace had it cleared */
+ if (!(current->thread.mmcr0 & MMCR0_PMXE))
+ mmcr0 &= ~MMCR0_PMXE;
+
+ mtspr(SPRN_SIAR, current->thread.siar);
+ mtspr(SPRN_SIER, current->thread.sier);
+ mtspr(SPRN_SDAR, current->thread.sdar);
+ mtspr(SPRN_MMCR2, current->thread.mmcr2);
+out:
+ return mmcr0;
+}
#endif /* CONFIG_PPC64 */
static void perf_event_interrupt(struct pt_regs *regs);
@@ -734,6 +829,13 @@ static void power_pmu_read(struct perf_event *event)
if (!event->hw.idx)
return;
+
+ if (is_ebb_event(event)) {
+ val = read_pmc(event->hw.idx);
+ local64_set(&event->hw.prev_count, val);
+ return;
+ }
+
/*
* Performance monitor interrupts come even when interrupts
* are soft-disabled, as long as interrupts are hard-enabled.
@@ -854,7 +956,7 @@ static void write_mmcr0(struct cpu_hw_events *cpuhw, unsigned long mmcr0)
static void power_pmu_disable(struct pmu *pmu)
{
struct cpu_hw_events *cpuhw;
- unsigned long flags, val;
+ unsigned long flags, mmcr0, val;
if (!ppmu)
return;
@@ -871,11 +973,11 @@ static void power_pmu_disable(struct pmu *pmu)
}
/*
- * Set the 'freeze counters' bit, clear PMAO/FC56.
+ * Set the 'freeze counters' bit, clear EBE/PMCC/PMAO/FC56.
*/
- val = mfspr(SPRN_MMCR0);
+ val = mmcr0 = mfspr(SPRN_MMCR0);
val |= MMCR0_FC;
- val &= ~(MMCR0_PMAO | MMCR0_FC56);
+ val &= ~(MMCR0_EBE | MMCR0_PMCC | MMCR0_PMAO | MMCR0_FC56);
/*
* The barrier is to make sure the mtspr has been
@@ -896,7 +998,10 @@ static void power_pmu_disable(struct pmu *pmu)
cpuhw->disabled = 1;
cpuhw->n_added = 0;
+
+ ebb_switch_out(mmcr0);
}
+
local_irq_restore(flags);
}
@@ -911,15 +1016,15 @@ static void power_pmu_enable(struct pmu *pmu)
struct cpu_hw_events *cpuhw;
unsigned long flags;
long i;
- unsigned long val;
+ unsigned long val, mmcr0;
s64 left;
unsigned int hwc_index[MAX_HWEVENTS];
int n_lim;
int idx;
+ bool ebb;
if (!ppmu)
return;
-
local_irq_save(flags);
cpuhw = &__get_cpu_var(cpu_hw_events);
@@ -934,6 +1039,13 @@ static void power_pmu_enable(struct pmu *pmu)
cpuhw->disabled = 0;
/*
+ * EBB requires an exclusive group and all events must have the EBB
+ * flag set, or not set, so we can just check a single event. Also we
+ * know we have at least one event.
+ */
+ ebb = is_ebb_event(cpuhw->event[0]);
+
+ /*
* If we didn't change anything, or only removed events,
* no need to recalculate MMCR* settings and reset the PMCs.
* Just reenable the PMU with the current MMCR* settings
@@ -1008,25 +1120,34 @@ static void power_pmu_enable(struct pmu *pmu)
++n_lim;
continue;
}
- val = 0;
- if (event->hw.sample_period) {
- left = local64_read(&event->hw.period_left);
- if (left < 0x80000000L)
- val = 0x80000000L - left;
+
+ if (ebb)
+ val = local64_read(&event->hw.prev_count);
+ else {
+ val = 0;
+ if (event->hw.sample_period) {
+ left = local64_read(&event->hw.period_left);
+ if (left < 0x80000000L)
+ val = 0x80000000L - left;
+ }
+ local64_set(&event->hw.prev_count, val);
}
- local64_set(&event->hw.prev_count, val);
+
event->hw.idx = idx;
if (event->hw.state & PERF_HES_STOPPED)
val = 0;
write_pmc(idx, val);
+
perf_event_update_userpage(event);
}
cpuhw->n_limited = n_lim;
cpuhw->mmcr[0] |= MMCR0_PMXE | MMCR0_FCECE;
out_enable:
+ mmcr0 = ebb_switch_in(ebb, cpuhw->mmcr[0]);
+
mb();
- write_mmcr0(cpuhw, cpuhw->mmcr[0]);
+ write_mmcr0(cpuhw, mmcr0);
/*
* Enable instruction sampling if necessary
@@ -1124,6 +1245,8 @@ static int power_pmu_add(struct perf_event *event, int ef_flags)
event->hw.config = cpuhw->events[n0];
nocheck:
+ ebb_event_add(event);
+
++cpuhw->n_events;
++cpuhw->n_added;
@@ -1484,6 +1607,11 @@ static int power_pmu_event_init(struct perf_event *event)
}
}
+ /* Extra checks for EBB */
+ err = ebb_event_check(event);
+ if (err)
+ return err;
+
/*
* If this is in a group, check if it can go on with all the
* other hardware events in the group. We assume the event
@@ -1523,6 +1651,13 @@ static int power_pmu_event_init(struct perf_event *event)
local64_set(&event->hw.period_left, event->hw.last_period);
/*
+ * For EBB events we just context switch the PMC value, we don't do any
+ * of the sample_period logic. We use hw.prev_count for this.
+ */
+ if (is_ebb_event(event))
+ local64_set(&event->hw.prev_count, 0);
+
+ /*
* See if we need to reserve the PMU.
* If no events are currently in use, then we have to take a
* mutex to ensure that we don't race with another task doing
--
1.7.10.4
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