Feature request: Conditionally submit a Zone.

[mcourteaux]

Looking at the code of tracy::ScopedZone, it doesn't seem possible to conditionally submit/commit a zone, as the constructor already commits something right away.

My situation: I'm having a spinlock where some threads are waiting for other threads. I'd like to catch outliers in case the spinlock takes unusually long. In that case I do want to pay the communication overhead of sending the Zone, otherwise, I'd like to just discard it.

Ideally, I could change the zone name from "spinlock" to "unusually_long_spinlock" or something, you see? From my 5.7 million spinlock Zones, about 4.9 million are very short (< 3 microseconds):

I'm timing the length of the spinlock myself using rdtsc for other statistics, so I could use that. To control it. However, a macro of some sorts that allows me to delete a zone would be cool.

[wolfpld]

The stream must be temporally coherent, and what you are asking would violate that requirement. You may want to implement your own discardable variant of a zone that would postpone sending the begin event, but that has big caveats you need to understand.

[mcourteaux]

I am assuming "temporally coherent" means "monotonically increasing in time"? It would only violate this requirement if the Zone has child Zones, right? Otherwise, delaying submitting the beginning of a Zone, doesn't break the monotonicity of things. UNLESS the sampling data comes into the same stream and also has to be monotonically increasing relative to the other events (such as the Zones).

[wolfpld]

Child zones are the main concern here. Sampling data is already disjoint because it is accumulated in kernel buffers and then processed in batches that cover past or future events.

[mcourteaux]

Okay, so it should work if I don't create child zones? I might give that a try soon. Will report back on the success of this. Thanks for the quick responses. :smile:

[wolfpld]

Yes, it should be fairly simple to do. The API may change at some point in the future, but I don't have any immediate plans to do so.

[mcourteaux]

I quickly put this stuff together. Nothing fancy. If you have feedback, I could turn this into a PR, if you are interested:

#pragma once

#include <limits>
#include <stdint.h>
#include <string.h>

#include "../public/client/TracyProfiler.hpp"
#include "../public/common/TracyAlign.hpp"
#include "../public/common/TracyAlloc.hpp"
#include "../public/common/TracySystem.hpp"

#if TRACY_ENABLE

#define ConditionalZoneNamedN( varname, name, active, discard_if_faster_than_this ) static constexpr tracy::SourceLocationData TracyConcat(__tracy_source_location,TracyLine) { name, TracyFunction,  TracyFile, (uint32_t)TracyLine, 0 }; tracy::ScopedConditionalZone varname( &TracyConcat(__tracy_source_location,TracyLine), discard_if_faster_than_this, active )
#define ConditionalZoneScopedN( name, discard_if_faster_than_this ) ConditionalZoneNamedN( ___tracy_scoped_zone, name, true, discard_if_faster_than_this )


namespace tracy {

class ScopedConditionalZone {
 public:
  ScopedConditionalZone(const ScopedConditionalZone &) = delete;
  ScopedConditionalZone(ScopedConditionalZone &&) = delete;
  ScopedConditionalZone &operator=(const ScopedConditionalZone &) = delete;
  ScopedConditionalZone &operator=(ScopedConditionalZone &&) = delete;

  ScopedConditionalZone(const SourceLocationData *srcloc, int64_t discard_if_faster_than_this, bool is_active = true)
#ifdef TRACY_ON_DEMAND
      : m_active(is_active && GetProfiler().IsConnected()), m_discard_if_faster_than_this(discard_if_faster_than_this), m_srcloc((uint64_t)srcloc)
#else
      : m_active(is_active), m_discard_if_faster_than_this(discard_if_faster_than_this), m_srcloc((uint64_t)srcloc)
#endif
  {
    if (!m_active)
      return;
#ifdef TRACY_ON_DEMAND
    m_connectionId = GetProfiler().ConnectionId();
#endif

    m_zone_begin = Profiler::GetTime();
  }

  ~ScopedConditionalZone() {
    if (!m_active)
      return;
#ifdef TRACY_ON_DEMAND
    if (GetProfiler().ConnectionId() != m_connectionId)
      return;
#endif
    int64_t end_time = Profiler::GetTime();
    int64_t duration = end_time - m_zone_begin;
    if (duration < m_discard_if_faster_than_this) {
      return;
    }
    {
      TracyQueuePrepare(QueueType::ZoneBegin);
      MemWrite(&item->zoneBegin.time, m_zone_begin);
      MemWrite(&item->zoneBegin.srcloc, m_srcloc);
      TracyQueueCommit(zoneBeginThread);
    }

    {
      TracyQueuePrepare(QueueType::ZoneEnd);
      MemWrite(&item->zoneEnd.time, end_time);
      TracyQueueCommit(zoneEndThread);
    }
  }

  // Delete all the fancy features, to prevent storing too much info.
  tracy_force_inline void Text(const char *txt, size_t size) = delete;
  tracy_force_inline void Name(const char *txt, size_t size) = delete;
  tracy_force_inline void Value(uint64_t value) = delete;


  tracy_force_inline bool IsActive() const { return m_active; }

 private:
  const bool m_active;
  int64_t m_discard_if_faster_than_this;
  int64_t m_zone_begin;
  uint64_t m_srcloc;

#ifdef TRACY_ON_DEMAND
  uint64_t m_connectionId;
#endif
};
} // namespace tracy
#else



#endif

[wolfpld]

I could turn this into a PR

I don't think this is something that should be provided by default.