From 807ea52b02aa761c4e864d4850956c2c90cf346b Mon Sep 17 00:00:00 2001
From: Geoffrey McRae <geoff@hostfission.com>
Date: Thu, 6 Aug 2026 17:34:25 +1000
Subject: [PATCH] [idd] scheduler: reject isolated work timing stalls

---
 idd/LGIdd/CFrameScheduler.cpp | 34 +++++++++++++++++++++++++++++++---
 idd/LGIdd/CFrameScheduler.h   | 16 ++++++++++------
 2 files changed, 41 insertions(+), 9 deletions(-)

diff --git a/idd/LGIdd/CFrameScheduler.cpp b/idd/LGIdd/CFrameScheduler.cpp
index 4eefa867..3e20db3a 100644
--- a/idd/LGIdd/CFrameScheduler.cpp
+++ b/idd/LGIdd/CFrameScheduler.cpp
@@ -260,6 +260,9 @@ void CFrameScheduler::Reset()
   m_lastArrival       = 0;
   m_guestPeriod       = 0;
   m_workEstimate      = 0;
+  memset(m_workTiming, 0, sizeof(m_workTiming));
+  m_workTimingCount   = 0;
+  m_workTimingIndex   = 0;
   m_nextDeadline      = 0;
   m_deadlineSerial    = 0;
   m_pendingCorrection = 0;
@@ -1017,10 +1020,35 @@ void CFrameScheduler::TryRecordFrameTiming(uint64_t duration)
   if (!TryAcquireSRWLockExclusive(&m_lock))
     return;
 
-  if (!m_workEstimate || duration > m_workEstimate)
-    m_workEstimate = duration;
+  m_workTiming[m_workTimingIndex] = duration;
+  m_workTimingIndex =
+    (m_workTimingIndex + 1) % WORK_TIMING_HISTORY_SIZE;
+  if (m_workTimingCount < WORK_TIMING_HISTORY_SIZE)
+    ++m_workTimingCount;
+
+  uint64_t sorted[WORK_TIMING_HISTORY_SIZE];
+  memcpy(sorted, m_workTiming,
+    m_workTimingCount * sizeof(*sorted));
+  for (unsigned i = 1; i < m_workTimingCount; ++i)
+  {
+    const uint64_t sample = sorted[i];
+    unsigned       j      = i;
+    while (j && sorted[j - 1] > sample)
+    {
+      sorted[j] = sorted[j - 1];
+      --j;
+    }
+    sorted[j] = sample;
+  }
+
+  if (m_workTimingCount == 1)
+    m_workEstimate = sorted[0];
   else
-    m_workEstimate = (m_workEstimate * 31 + duration) / 32;
+  {
+    const unsigned discarded = min(m_workTimingCount - 1,
+      max(1U, m_workTimingCount / 10));
+    m_workEstimate = sorted[m_workTimingCount - discarded - 1];
+  }
 
   ReleaseSRWLockExclusive(&m_lock);
 }
diff --git a/idd/LGIdd/CFrameScheduler.h b/idd/LGIdd/CFrameScheduler.h
index 3c685531..b3cde9c6 100644
--- a/idd/LGIdd/CFrameScheduler.h
+++ b/idd/LGIdd/CFrameScheduler.h
@@ -80,6 +80,7 @@ private:
   };
 
   static const unsigned PUBLICATION_HISTORY_SIZE = 128;
+  static const unsigned WORK_TIMING_HISTORY_SIZE  = 32;
 
   mutable SRWLOCK m_lock = SRWLOCK_INIT;
   HANDLE          m_wakeEvent = nullptr;
@@ -94,12 +95,15 @@ private:
   uint64_t m_republishRequestTicket = 0;
   uint64_t m_republishAckTicket     = 0;
 
-  uint64_t m_lastArrival             = 0;
-  uint64_t m_guestPeriod             = 0;
-  uint64_t m_workEstimate            = 0;
-  uint64_t m_nextDeadline            = 0;
-  uint32_t m_deadlineSerial          = 0;
-  int64_t  m_pendingCorrection       = 0;
+  uint64_t m_lastArrival                          = 0;
+  uint64_t m_guestPeriod                          = 0;
+  uint64_t m_workEstimate                         = 0;
+  uint64_t m_workTiming[WORK_TIMING_HISTORY_SIZE] = {};
+  unsigned m_workTimingCount                      = 0;
+  unsigned m_workTimingIndex                      = 0;
+  uint64_t m_nextDeadline                         = 0;
+  uint32_t m_deadlineSerial                       = 0;
+  int64_t  m_pendingCorrection                    = 0;
 
   Publication m_publications[PUBLICATION_HISTORY_SIZE] = {};
   unsigned    m_publicationIndex                       = 0;