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Subject[V3][PATCH 6/7] perf, x86: Implement 64 bit counter support for IBS
Date
This patch implements 64 bit counter support for IBS. The sampling
period is no longer limited to the hw counter width.

The functions perf_event_set_period() and perf_event_try_update() can
be used as generic functions. They can replace similar code that is
duplicate across architectures.

V2: Added caps check for IBS_OP_CUR_CNT emulation.

Signed-off-by: Robert Richter <robert.richter@amd.com>
---
arch/x86/include/asm/perf_event.h | 2 +
arch/x86/kernel/cpu/perf_event_amd_ibs.c | 204 +++++++++++++++++++++++++++---
2 files changed, 185 insertions(+), 21 deletions(-)

diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index e7d2f15..cc44a1a 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -150,6 +150,8 @@ union cpuid10_edx {
#define IBS_FETCH_MAX_CNT 0x0000FFFFULL

/* IbsOpCtl bits */
+/* lower 4 bits of the current count are ignored: */
+#define IBS_OP_CUR_CNT (0xFFFF0ULL<<32)
#define IBS_OP_CNT_CTL (1ULL<<19)
#define IBS_OP_VAL (1ULL<<18)
#define IBS_OP_ENABLE (1ULL<<17)
diff --git a/arch/x86/kernel/cpu/perf_event_amd_ibs.c b/arch/x86/kernel/cpu/perf_event_amd_ibs.c
index 9713d31..6deb4d9 100644
--- a/arch/x86/kernel/cpu/perf_event_amd_ibs.c
+++ b/arch/x86/kernel/cpu/perf_event_amd_ibs.c
@@ -42,9 +42,11 @@ struct perf_ibs {
u64 cnt_mask;
u64 enable_mask;
u64 valid_mask;
+ u64 max_period;
unsigned long offset_mask[1];
int offset_max;
struct cpu_perf_ibs __percpu *pcpu;
+ u64 (*get_count)(u64 config);
};

struct perf_ibs_data {
@@ -56,6 +58,78 @@ struct perf_ibs_data {
u64 regs[MSR_AMD64_IBS_REG_COUNT_MAX];
};

+static int
+perf_event_set_period(struct hw_perf_event *hwc, u64 min, u64 max, u64 *count)
+{
+ s64 left = local64_read(&hwc->period_left);
+ s64 period = hwc->sample_period;
+ int overflow = 0;
+
+ /*
+ * If we are way outside a reasonable range then just skip forward:
+ */
+ if (unlikely(left <= -period)) {
+ left = period;
+ local64_set(&hwc->period_left, left);
+ hwc->last_period = period;
+ overflow = 1;
+ }
+
+ if (unlikely(left <= 0)) {
+ left += period;
+ local64_set(&hwc->period_left, left);
+ hwc->last_period = period;
+ overflow = 1;
+ }
+
+ if (unlikely(left < min))
+ left = min;
+
+ if (left > max)
+ left = max;
+
+ *count = (u64)left;
+
+ return overflow;
+}
+
+static int
+perf_event_try_update(struct perf_event *event, u64 new_raw_count, int width)
+{
+ struct hw_perf_event *hwc = &event->hw;
+ int shift = 64 - width;
+ u64 prev_raw_count;
+ u64 delta;
+
+ /*
+ * Careful: an NMI might modify the previous event value.
+ *
+ * Our tactic to handle this is to first atomically read and
+ * exchange a new raw count - then add that new-prev delta
+ * count to the generic event atomically:
+ */
+ prev_raw_count = local64_read(&hwc->prev_count);
+ if (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
+ new_raw_count) != prev_raw_count)
+ return 0;
+
+ /*
+ * Now we have the new raw value and have updated the prev
+ * timestamp already. We can now calculate the elapsed delta
+ * (event-)time and add that to the generic event.
+ *
+ * Careful, not all hw sign-extends above the physical width
+ * of the count.
+ */
+ delta = (new_raw_count << shift) - (prev_raw_count << shift);
+ delta >>= shift;
+
+ local64_add(delta, &event->count);
+ local64_sub(delta, &hwc->period_left);
+
+ return 1;
+}
+
static struct perf_ibs perf_ibs_fetch;
static struct perf_ibs perf_ibs_op;

@@ -89,18 +163,14 @@ static int perf_ibs_init(struct perf_event *event)
if (hwc->sample_period & 0x0f)
/* lower 4 bits can not be set in ibs max cnt */
return -EINVAL;
- max_cnt = hwc->sample_period >> 4;
- if (max_cnt & ~perf_ibs->cnt_mask)
- /* out of range */
- return -EINVAL;
- config |= max_cnt;
} else {
max_cnt = config & perf_ibs->cnt_mask;
+ config &= ~perf_ibs->cnt_mask;
event->attr.sample_period = max_cnt << 4;
hwc->sample_period = event->attr.sample_period;
}

- if (!max_cnt)
+ if (!hwc->sample_period)
return -EINVAL;

hwc->config_base = perf_ibs->msr;
@@ -109,16 +179,71 @@ static int perf_ibs_init(struct perf_event *event)
return 0;
}

+static int perf_ibs_set_period(struct perf_ibs *perf_ibs,
+ struct hw_perf_event *hwc, u64 *period)
+{
+ int ret;
+
+ /* ignore lower 4 bits in min count: */
+ ret = perf_event_set_period(hwc, 1<<4, perf_ibs->max_period, period);
+ local64_set(&hwc->prev_count, 0);
+
+ return ret;
+}
+
+static u64 get_ibs_fetch_count(u64 config)
+{
+ return (config & IBS_FETCH_CNT) >> 12;
+}
+
+static u64 get_ibs_op_count(u64 config)
+{
+ return (config & IBS_OP_CUR_CNT) >> 32;
+}
+
+static void
+perf_ibs_event_update(struct perf_ibs *perf_ibs, struct perf_event *event,
+ u64 config)
+{
+ u64 count = perf_ibs->get_count(config);
+
+ while (!perf_event_try_update(event, count, 20)) {
+ rdmsrl(event->hw.config_base, config);
+ count = perf_ibs->get_count(config);
+ }
+}
+
+/* Note: The enable mask must be encoded in the config argument. */
+static inline void perf_ibs_enable_event(struct hw_perf_event *hwc, u64 config)
+{
+ wrmsrl(hwc->config_base, hwc->config | config);
+}
+
+/*
+ * We cannot restore the ibs pmu state, so we always needs to update
+ * the event while stopping it and then reset the state when starting
+ * again. Thus, ignoring PERF_EF_RELOAD and PERF_EF_UPDATE flags in
+ * perf_ibs_start()/perf_ibs_stop() and instead always do it.
+ */
static void perf_ibs_start(struct perf_event *event, int flags)
{
struct hw_perf_event *hwc = &event->hw;
struct perf_ibs *perf_ibs = container_of(event->pmu, struct perf_ibs, pmu);
struct cpu_perf_ibs *pcpu = this_cpu_ptr(perf_ibs->pcpu);
+ u64 config;

- if (test_and_set_bit(IBS_STARTED, pcpu->state))
+ if (WARN_ON_ONCE(!(hwc->state & PERF_HES_STOPPED)))
return;

- wrmsrl(hwc->config_base, hwc->config | perf_ibs->enable_mask);
+ WARN_ON_ONCE(!(hwc->state & PERF_HES_UPTODATE));
+ hwc->state = 0;
+
+ perf_ibs_set_period(perf_ibs, hwc, &config);
+ config = (config >> 4) | perf_ibs->enable_mask;
+ set_bit(IBS_STARTED, pcpu->state);
+ perf_ibs_enable_event(hwc, config);
+
+ perf_event_update_userpage(event);
}

static void perf_ibs_stop(struct perf_event *event, int flags)
@@ -127,15 +252,28 @@ static void perf_ibs_stop(struct perf_event *event, int flags)
struct perf_ibs *perf_ibs = container_of(event->pmu, struct perf_ibs, pmu);
struct cpu_perf_ibs *pcpu = this_cpu_ptr(perf_ibs->pcpu);
u64 val;
+ int stopping;

- if (!test_and_clear_bit(IBS_STARTED, pcpu->state))
- return;
+ stopping = test_and_clear_bit(IBS_STARTED, pcpu->state);

- set_bit(IBS_STOPPING, pcpu->state);
+ if (!stopping && (hwc->state & PERF_HES_UPTODATE))
+ return;

rdmsrl(hwc->config_base, val);
- val &= ~perf_ibs->enable_mask;
- wrmsrl(hwc->config_base, val);
+
+ if (stopping) {
+ set_bit(IBS_STOPPING, pcpu->state);
+ val &= ~perf_ibs->enable_mask;
+ wrmsrl(hwc->config_base, val);
+ WARN_ON_ONCE(hwc->state & PERF_HES_STOPPED);
+ hwc->state |= PERF_HES_STOPPED;
+ }
+
+ if (hwc->state & PERF_HES_UPTODATE)
+ return;
+
+ perf_ibs_event_update(perf_ibs, event, val);
+ hwc->state |= PERF_HES_UPTODATE;
}

static int perf_ibs_add(struct perf_event *event, int flags)
@@ -146,6 +284,8 @@ static int perf_ibs_add(struct perf_event *event, int flags)
if (test_and_set_bit(IBS_ENABLED, pcpu->state))
return -ENOSPC;

+ event->hw.state = PERF_HES_UPTODATE | PERF_HES_STOPPED;
+
pcpu->event = event;

if (flags & PERF_EF_START)
@@ -162,9 +302,11 @@ static void perf_ibs_del(struct perf_event *event, int flags)
if (!test_and_clear_bit(IBS_ENABLED, pcpu->state))
return;

- perf_ibs_stop(event, 0);
+ perf_ibs_stop(event, PERF_EF_UPDATE);

pcpu->event = NULL;
+
+ perf_event_update_userpage(event);
}

static void perf_ibs_read(struct perf_event *event) { }
@@ -185,8 +327,11 @@ static struct perf_ibs perf_ibs_fetch = {
.cnt_mask = IBS_FETCH_MAX_CNT,
.enable_mask = IBS_FETCH_ENABLE,
.valid_mask = IBS_FETCH_VAL,
+ .max_period = IBS_FETCH_MAX_CNT << 4,
.offset_mask = { MSR_AMD64_IBSFETCH_REG_MASK },
.offset_max = MSR_AMD64_IBSFETCH_REG_COUNT,
+
+ .get_count = get_ibs_fetch_count,
};

static struct perf_ibs perf_ibs_op = {
@@ -205,8 +350,11 @@ static struct perf_ibs perf_ibs_op = {
.cnt_mask = IBS_OP_MAX_CNT,
.enable_mask = IBS_OP_ENABLE,
.valid_mask = IBS_OP_VAL,
+ .max_period = IBS_OP_MAX_CNT << 4,
.offset_mask = { MSR_AMD64_IBSOP_REG_MASK },
.offset_max = MSR_AMD64_IBSOP_REG_COUNT,
+
+ .get_count = get_ibs_op_count,
};

static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs)
@@ -218,9 +366,9 @@ static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs)
struct perf_raw_record raw;
struct pt_regs regs;
struct perf_ibs_data ibs_data;
- int offset, size;
+ int offset, size, overflow, reenable;
unsigned int msr;
- u64 *buf;
+ u64 *buf, config;

if (!test_bit(IBS_STARTED, pcpu->state)) {
/* Catch spurious interrupts after stopping IBS: */
@@ -255,11 +403,25 @@ static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs)

regs = *iregs; /* XXX: update ip from ibs sample */

- if (perf_event_overflow(event, &data, &regs))
- ; /* stop */
- else
- /* reenable */
- wrmsrl(hwc->config_base, hwc->config | perf_ibs->enable_mask);
+ /*
+ * Emulate IbsOpCurCnt in MSRC001_1033 (IbsOpCtl), not
+ * supported in all cpus. As this triggered an interrupt, we
+ * set the current count to the max count.
+ */
+ config = ibs_data.regs[0];
+ if (perf_ibs == &perf_ibs_op && !(ibs_caps & IBS_CAPS_RDWROPCNT)) {
+ config &= ~IBS_OP_CUR_CNT;
+ config |= (config & IBS_OP_MAX_CNT) << 36;
+ }
+
+ perf_ibs_event_update(perf_ibs, event, config);
+
+ overflow = perf_ibs_set_period(perf_ibs, hwc, &config);
+ reenable = !(overflow && perf_event_overflow(event, &data, &regs));
+ config = (config >> 4) | (reenable ? perf_ibs->enable_mask : 0);
+ perf_ibs_enable_event(hwc, config);
+
+ perf_event_update_userpage(event);

return 1;
}
--
1.7.6.1



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