Re: [Intel-gfx] [PATCH 1/1] i915/query: Correlate engine and cpu timestamps with better accuracy

[Lionel Landwerlin <lionel.g.landwerlin@intel.com>]

On 23/04/2021 18:11, Umesh Nerlige Ramappa wrote:
> On Fri, Apr 23, 2021 at 10:05:34AM +0300, Lionel Landwerlin wrote:
>> On 21/04/2021 20:28, Umesh Nerlige Ramappa wrote:
>>> 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.
>>>
>>> Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
>>> ---
>>>  drivers/gpu/drm/i915/i915_query.c | 145 ++++++++++++++++++++++++++++++
>>>  include/uapi/drm/i915_drm.h       |  48 ++++++++++
>>>  2 files changed, 193 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/i915/i915_query.c 
>>> b/drivers/gpu/drm/i915/i915_query.c
>>> index fed337ad7b68..25b96927ab92 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 +92,148 @@ 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,
>>> +          __ktime_func_t cpu_clock)
>>> +{
>>> +    u32 upper, lower, old_upper, loop = 0;
>>> +
>>> +    upper = intel_uncore_read_fw(uncore, upper_reg);
>>> +    do {
>>> +        cpu_ts[1] = local_clock();
>>> +        cpu_ts[0] = cpu_clock();
>>> +        lower = intel_uncore_read_fw(uncore, lower_reg);
>>> +        cpu_ts[1] = local_clock() - cpu_ts[1];
>>> +        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,
>>> +          __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_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;
>>> +    int ret;
>>> +
>>> +    if (INTEL_GEN(i915) < 6)
>>> +        return -ENODEV;
>
> Less than gen6 is handled here early on.
>
>>> +
>>> +    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 (IS_GEN(i915, 6) &&
>>> +        query.engine.engine_class != I915_ENGINE_CLASS_RENDER)
>>> +        return -ENODEV;
>>
>>
>> Thanks a bunch for rebasing this.
>>
>> My only comment on this patch would be : don't we want 
>> IS_GEN_RANGE(i915, 1, 6) instead of IS_GEN(i915, 6) ?
>>
>> (assuming gen1 is a thing...)
>
> Less than gen6 check is above at function entry. On gen6, only render 
> works, so I wait until I can get the engine to check that.


Ah okay, I thought we could go for parity with REG_READ which seems to 
go back to Gen4.

But it's not important at least for mesa because we probably only case 
about gen7+.


Hopefuly nobody else has objections :


Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>


Thanks,


-Lionel


>
> Thanks,
> Umesh
>
>>
>>
>> -Lionel
>>
>>
>>> +
>>> +    query.cs_frequency = engine->gt->clock_frequency;
>>> +    ret = __query_cs_cycles(engine,
>>> +                &query.cs_cycles,
>>> +                query.cpu_timestamp,
>>> +                cpu_clock);
>>> +    if (ret)
>>> +        return ret;
>>> +
>>> +    if (put_user(query.cs_frequency, &query_ptr->cs_frequency))
>>> +        return -EFAULT;
>>> +
>>> +    if (put_user(query.cpu_timestamp[0], 
>>> &query_ptr->cpu_timestamp[0]))
>>> +        return -EFAULT;
>>> +
>>> +    if (put_user(query.cpu_timestamp[1], 
>>> &query_ptr->cpu_timestamp[1]))
>>> +        return -EFAULT;
>>> +
>>> +    if (put_user(query.cs_cycles, &query_ptr->cs_cycles))
>>> +        return -EFAULT;
>>> +
>>> +    return sizeof(query);
>>> +}
>>> +
>>>  static int
>>>  query_engine_info(struct drm_i915_private *i915,
>>>            struct drm_i915_query_item *query_item)
>>> @@ -424,6 +568,7 @@ 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..08b00f1709b5 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 +2401,50 @@ struct drm_i915_engine_info {
>>>      __u64 rsvd1[4];
>>>  };
>>> +/**
>>> + * struct drm_i915_query_cs_cycles
>>> + *
>>> + * The query returns the command streamer cycles and the frequency 
>>> that can be
>>> + * used to calculate the command streamer timestamp. In addition 
>>> the query
>>> + * returns a set of cpu timestamps that indicate when the command 
>>> streamer cycle
>>> + * count was captured.
>>> + */
>>> +struct drm_i915_query_cs_cycles {
>>> +    /** Engine for which command streamer cycles is queried. */
>>> +    struct i915_engine_class_instance engine;
>>> +
>>> +    /** Must be zero. */
>>> +    __u32 flags;
>>> +
>>> +    /**
>>> +     * Command streamer cycles as read from the command streamer
>>> +     * register at 0x358 offset.
>>> +     */
>>> +    __u64 cs_cycles;
>>> +
>>> +    /** Frequency of the cs cycles in Hz. */
>>> +    __u64 cs_frequency;
>>> +
>>> +    /**
>>> +     * CPU timestamps in ns. cpu_timestamp[0] is captured before 
>>> reading the
>>> +     * cs_cycles register using the reference clockid set by the user.
>>> +     * cpu_timestamp[1] is the time taken in ns to read the lower 
>>> dword of
>>> +     * the cs_cycles register.
>>> +     */
>>> +    __u64 cpu_timestamp[2];
>>> +
>>> +    /**
>>> +     * 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;
>>> +
>>> +    /** Must be zero. */
>>> +    __u32 rsvd;
>>> +};
>>> +
>>>  /**
>>>   * struct drm_i915_query_engine_info
>>>   *
>>
>>

_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx