[PATCH 7/7] perf, x86: Implement 64 bit counter support for IBS

[Robert Richter]

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.

Signed-off-by: Robert Richter <robert.richter@xxxxxxx>
---
 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 ea9f360..bd78994 100644
--- a/arch/x86/kernel/cpu/perf_event_amd_ibs.c
+++ b/arch/x86/kernel/cpu/perf_event_amd_ibs.c
@@ -40,10 +40,84 @@ struct perf_ibs {
 	u64		cnt_mask;
 	u64		enable_mask;
 	u64		valid_mask;
+	u64		max_period;
 	int		reg_count;
 	struct cpu_perf_ibs __percpu *pcpu;
+	u64		(*get_count)(u64 config);
 };
 
+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;
 
@@ -77,18 +151,14 @@ 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;
@@ -97,16 +167,71 @@ 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)
@@ -115,15 +240,28 @@ 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)
@@ -134,6 +272,8 @@ 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)
@@ -150,9 +290,11 @@ 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) { }
@@ -171,7 +313,10 @@ 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,
 	.reg_count		= MSR_AMD64_IBSFETCH_REG_COUNT,
+
+	.get_count		= get_ibs_fetch_count,
 };
 
 static struct perf_ibs perf_ibs_op = {
@@ -188,7 +333,10 @@ 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,
 	.reg_count		= 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)
@@ -200,9 +348,9 @@ static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs)
 	struct perf_raw_record raw;
 	struct pt_regs regs;
 	u64 buffer[MSR_AMD64_IBS_REG_COUNT_MAX];
-	int i;
+	int i, overflow, reenable;
 	unsigned int msr;
-	u64 *buf;
+	u64 *buf, config;
 
 	if (!test_bit(IBS_STARTED, pcpu->state)) {
 		/* Catch spurious interrupts after stopping IBS: */
@@ -229,11 +377,25 @@ 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 = buffer[0];
+	if (perf_ibs == &perf_ibs_op) {
+		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;
 }
-- 
1.7.5.3


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/