[PATCH 1/1] i915/query: Correlate engine and cpu timestamps with better accuracy
Umesh Nerlige Ramappa
umesh.nerlige.ramappa at intel.com
Tue May 4 00:12:13 UTC 2021
Perf measurements rely on CPU and engine timestamps to correlate
events of interest across these time domains. Current mechanisms get
these timestamps separately and the calculated delta between these
timestamps lack enough accuracy.
To improve the accuracy of these time measurements to within a few us,
add a query that returns the engine and cpu timestamps captured as
close to each other as possible.
v2: (Tvrtko)
- document clock reference used
- return cpu timestamp always
- capture cpu time just before lower dword of cs timestamp
v3: (Chris)
- use uncore-rpm
- use __query_cs_timestamp helper
v4: (Lionel)
- Kernel perf subsytem allows users to specify the clock id to be used
in perf_event_open. This clock id is used by the perf subsystem to
return the appropriate cpu timestamp in perf events. Similarly, let
the user pass the clockid to this query so that cpu timestamp
corresponds to the clock id requested.
v5: (Tvrtko)
- Use normal ktime accessors instead of fast versions
- Add more uApi documentation
v6: (Lionel)
- Move switch out of spinlock
v7: (Chris)
- cs_timestamp is a misnomer, use cs_cycles instead
- return the cs cycle frequency as well in the query
v8:
- Add platform and engine specific checks
v9: (Lionel)
- Return 2 cpu timestamps in the query - captured before and after the
register read
v10: (Chris)
- Use local_clock() to measure time taken to read lower dword of
register and return it to user.
v11: (Jani)
- IS_GEN deprecated. User GRAPHICS_VER instead.
v12: (Jason)
- Split cpu timestamp array into timestamp and delta for cleaner API
v13:
- Return the width of cs cycles
- Conform to kernel doc format
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>
---
drivers/gpu/drm/i915/i915_query.c | 157 ++++++++++++++++++++++++++++++
include/uapi/drm/i915_drm.h | 56 +++++++++++
2 files changed, 213 insertions(+)
diff --git a/drivers/gpu/drm/i915/i915_query.c b/drivers/gpu/drm/i915/i915_query.c
index fed337ad7b68..2e7039c71866 100644
--- a/drivers/gpu/drm/i915/i915_query.c
+++ b/drivers/gpu/drm/i915/i915_query.c
@@ -6,6 +6,8 @@
#include <linux/nospec.h>
+#include "gt/intel_engine_pm.h"
+#include "gt/intel_engine_user.h"
#include "i915_drv.h"
#include "i915_perf.h"
#include "i915_query.h"
@@ -90,6 +92,160 @@ static int query_topology_info(struct drm_i915_private *dev_priv,
return total_length;
}
+typedef u64 (*__ktime_func_t)(void);
+static __ktime_func_t __clock_id_to_func(clockid_t clk_id)
+{
+ /*
+ * Use logic same as the perf subsystem to allow user to select the
+ * reference clock id to be used for timestamps.
+ */
+ switch (clk_id) {
+ case CLOCK_MONOTONIC:
+ return &ktime_get_ns;
+ case CLOCK_MONOTONIC_RAW:
+ return &ktime_get_raw_ns;
+ case CLOCK_REALTIME:
+ return &ktime_get_real_ns;
+ case CLOCK_BOOTTIME:
+ return &ktime_get_boottime_ns;
+ case CLOCK_TAI:
+ return &ktime_get_clocktai_ns;
+ default:
+ return NULL;
+ }
+}
+
+static inline int
+__read_timestamps(struct intel_uncore *uncore,
+ i915_reg_t lower_reg,
+ i915_reg_t upper_reg,
+ u64 *cs_ts,
+ u64 *cpu_ts,
+ u64 *cpu_delta,
+ __ktime_func_t cpu_clock)
+{
+ u32 upper, lower, old_upper, loop = 0;
+
+ upper = intel_uncore_read_fw(uncore, upper_reg);
+ do {
+ *cpu_delta = local_clock();
+ *cpu_ts = cpu_clock();
+ lower = intel_uncore_read_fw(uncore, lower_reg);
+ *cpu_delta = local_clock() - *cpu_delta;
+ old_upper = upper;
+ upper = intel_uncore_read_fw(uncore, upper_reg);
+ } while (upper != old_upper && loop++ < 2);
+
+ *cs_ts = (u64)upper << 32 | lower;
+
+ return 0;
+}
+
+static int
+__query_cs_cycles(struct intel_engine_cs *engine,
+ u64 *cs_ts, u64 *cpu_ts, u64 *cpu_delta,
+ __ktime_func_t cpu_clock)
+{
+ struct intel_uncore *uncore = engine->uncore;
+ enum forcewake_domains fw_domains;
+ u32 base = engine->mmio_base;
+ intel_wakeref_t wakeref;
+ int ret;
+
+ fw_domains = intel_uncore_forcewake_for_reg(uncore,
+ RING_TIMESTAMP(base),
+ FW_REG_READ);
+
+ with_intel_runtime_pm(uncore->rpm, wakeref) {
+ spin_lock_irq(&uncore->lock);
+ intel_uncore_forcewake_get__locked(uncore, fw_domains);
+
+ ret = __read_timestamps(uncore,
+ RING_TIMESTAMP(base),
+ RING_TIMESTAMP_UDW(base),
+ cs_ts,
+ cpu_ts,
+ cpu_delta,
+ cpu_clock);
+
+ intel_uncore_forcewake_put__locked(uncore, fw_domains);
+ spin_unlock_irq(&uncore->lock);
+ }
+
+ return ret;
+}
+
+static int
+query_cs_cycles(struct drm_i915_private *i915,
+ struct drm_i915_query_item *query_item)
+{
+ struct drm_i915_query_cs_cycles __user *query_ptr;
+ struct drm_i915_query_cs_cycles query;
+ struct intel_engine_cs *engine;
+ __ktime_func_t cpu_clock;
+ u32 width;
+ int ret;
+
+ if (GRAPHICS_VER(i915) < 6)
+ return -ENODEV;
+
+ query_ptr = u64_to_user_ptr(query_item->data_ptr);
+ ret = copy_query_item(&query, sizeof(query), sizeof(query), query_item);
+ if (ret != 0)
+ return ret;
+
+ if (query.flags)
+ return -EINVAL;
+
+ if (query.rsvd)
+ return -EINVAL;
+
+ cpu_clock = __clock_id_to_func(query.clockid);
+ if (!cpu_clock)
+ return -EINVAL;
+
+ engine = intel_engine_lookup_user(i915,
+ query.engine.engine_class,
+ query.engine.engine_instance);
+ if (!engine)
+ return -EINVAL;
+
+ if (GRAPHICS_VER(i915) == 6) {
+ if (query.engine.engine_class != I915_ENGINE_CLASS_RENDER)
+ return -ENODEV;
+
+ width = 32;
+ } else {
+ width = 36;
+ }
+
+ query.cs_frequency = engine->gt->clock_frequency;
+ ret = __query_cs_cycles(engine,
+ &query.cs_cycles,
+ &query.cpu_timestamp,
+ &query.cpu_delta,
+ cpu_clock);
+ if (ret)
+ return ret;
+
+ if (put_user(query.cs_frequency, &query_ptr->cs_frequency))
+ return -EFAULT;
+
+ if (put_user(query.cpu_timestamp, &query_ptr->cpu_timestamp))
+ return -EFAULT;
+
+ if (put_user(query.cpu_delta, &query_ptr->cpu_delta))
+ return -EFAULT;
+
+ if (put_user(query.cs_cycles, &query_ptr->cs_cycles))
+ return -EFAULT;
+
+ if (put_user(width, &query_ptr->width))
+ return -EFAULT;
+
+ return sizeof(query);
+}
+
static int
query_engine_info(struct drm_i915_private *i915,
struct drm_i915_query_item *query_item)
@@ -424,6 +580,7 @@ static int (* const i915_query_funcs[])(struct drm_i915_private *dev_priv,
query_topology_info,
query_engine_info,
query_perf_config,
+ query_cs_cycles,
};
int i915_query_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 6a34243a7646..17ac6135f9a7 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -2230,6 +2230,10 @@ struct drm_i915_query_item {
#define DRM_I915_QUERY_TOPOLOGY_INFO 1
#define DRM_I915_QUERY_ENGINE_INFO 2
#define DRM_I915_QUERY_PERF_CONFIG 3
+ /**
+ * Query Command Streamer timestamp register.
+ */
+#define DRM_I915_QUERY_CS_CYCLES 4
/* Must be kept compact -- no holes and well documented */
/**
@@ -2397,6 +2401,58 @@ struct drm_i915_engine_info {
__u64 rsvd1[4];
};
+/**
+ * struct drm_i915_query_cs_cycles
+ *
+ * The query returns the command streamer cycles, the frequency that can be
+ * used to calculate the command streamer timestamp, a cpu timestamp indicating
+ * when the cs cycles was captured and a cpu_delta capturing time taken to read
+ * the cs_cycles register.
+ */
+struct drm_i915_query_cs_cycles {
+ /** @engine: Engine for which command streamer cycles is queried. */
+ struct i915_engine_class_instance engine;
+
+ /** @flags: MBZ */
+ __u32 flags;
+
+ /**
+ * @cs_cycles: Command streamer cycles as read from the command streamer
+ * register at 0x358 offset.
+ */
+ __u64 cs_cycles;
+
+ /** @cs_frequency: Frequency of the cs cycles in Hz. */
+ __u64 cs_frequency;
+
+ /** @width: Width of the cs cycles in bits. */
+ __u64 width;
+
+ /**
+ * @cpu_timestamp: CPU timestamp in ns. The timestamp is captured before
+ * reading the cs_cycles register using the reference clockid set by the
+ * user.
+ */
+ __u64 cpu_timestamp;
+
+ /**
+ * @cpu_delta: Time delta in ns captured around reading the lower dword
+ * of the cs_cycles register.
+ */
+ __u64 cpu_delta;
+
+ /**
+ * @clockid: Reference clock id for CPU timestamp. For definition, see
+ * clock_gettime(2) and perf_event_open(2). Supported clock ids are
+ * CLOCK_MONOTONIC, CLOCK_MONOTONIC_RAW, CLOCK_REALTIME, CLOCK_BOOTTIME,
+ * CLOCK_TAI.
+ */
+ __s32 clockid;
+
+ /** @rsvd: MBZ */
+ __u32 rsvd;
+};
+
/**
* struct drm_i915_query_engine_info
*
--
2.20.1
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