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Share one ring per event kind and CPU in the sampling client

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Sampling events of one kind on one CPU now share a ring: the first
thread's event owns it, and the others are redirected into it with
PERF_EVENT_IOC_SET_OUTPUT. Redirected fds are kept open and enabled by
the worker.
This commit is contained in:
Lectem
2026-10-20 19:54:22 +02:00
parent b8935a8a56
commit 71d2513d0e
1 changed files with 37 additions and 9 deletions
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public/client/TracySysTrace.cpp
+37 -9
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@@ -420,10 +420,22 @@ struct SysTraceState
int ctxBufferIdx = 0;
bool ctxSwitchCallchain = false;
RingBuffer* ring = nullptr;
int* redirectFd = nullptr;
int numRedirectFd = 0;
};
static SysTraceState s_state;
// Sampling events of one kind on one CPU share a ring: the first thread's event owns it
// (the sharedRingFd array, per event kind and CPU), the others are redirected into it with
// PERF_EVENT_IOC_SET_OUTPUT. Redirected fds are kept open, and enabled by the worker.
static void CloseRedirectFds()
{
for( int i=0; i<s_state.numRedirectFd; i++ ) close( s_state.redirectFd[i] );
tracy_free( s_state.redirectFd );
s_state.redirectFd = nullptr;
s_state.numRedirectFd = 0;
}
struct PerfIterTarget
{
@@ -527,7 +539,7 @@ enum TraceEventId
static void ProbePreciseIp( perf_event_attr& pe, pid_t pid );
static bool OpenSampleEvent( const PerfIterTarget& tgt, const perf_event_attr& inPe, int eventId )
static bool OpenSampleEvent( const PerfIterTarget& tgt, const perf_event_attr& inPe, int eventId, int* sharedRingFd )
{
static bool noKernelAccessLogged = false;
perf_event_attr pe = inPe;
@@ -549,8 +561,15 @@ static bool OpenSampleEvent( const PerfIterTarget& tgt, const perf_event_attr& i
TracyDebug( " Failed to setup!" );
return false;
}
const int slot = eventId * s_state.numCpus + tgt.cpu;
if( sharedRingFd[slot] != -1 && ioctl( fd, PERF_EVENT_IOC_SET_OUTPUT, sharedRingFd[slot] ) == 0 )
{
s_state.redirectFd[s_state.numRedirectFd++] = fd;
return true;
}
new( s_state.ring + s_state.numBuffers ) RingBuffer( 64 * 1024, fd, eventId );
if( !s_state.ring[s_state.numBuffers].IsValid() ) return false;
if( sharedRingFd[slot] == -1 ) sharedRingFd[slot] = fd;
s_state.numBuffers++;
return true;
}
@@ -1066,6 +1085,10 @@ bool SysTraceStart( int64_t& samplingPeriod )
);
s_state.ring = (RingBuffer*)tracy_malloc( sizeof( RingBuffer ) * maxNumBuffers );
s_state.numBuffers = 0;
int* sharedRingFd = (int*)tracy_malloc( sizeof( int ) * EventVsync * s_state.numCpus );
for( int i=0; i<EventVsync*s_state.numCpus; i++ ) sharedRingFd[i] = -1;
s_state.redirectFd = (int*)tracy_malloc( sizeof( int ) * maxNumBuffers );
s_state.numRedirectFd = 0;
// software sampling
perf_event_attr pe = {};
@@ -1092,7 +1115,7 @@ bool SysTraceStart( int64_t& samplingPeriod )
ProbePreciseIp( pe, currentPid );
for( int i=0; i<numIter; i++ )
{
if( OpenSampleEvent( iter[i], pe, EventCallstack ) ) TracyDebug( " Target %i ok (EventCallstack)", i );
if( OpenSampleEvent( iter[i], pe, EventCallstack, sharedRingFd ) ) TracyDebug( " Target %i ok (EventCallstack)", i );
}
}
@@ -1120,13 +1143,13 @@ bool SysTraceStart( int64_t& samplingPeriod )
ProbePreciseIp( pe, PERF_COUNT_HW_CPU_CYCLES, PERF_COUNT_HW_INSTRUCTIONS, currentPid );
for( int i=0; i<numIter; i++ )
{
if( OpenSampleEvent( iter[i], pe, EventCpuCycles ) ) TracyDebug( " Target %i ok (EventCpuCycles)", i );
if( OpenSampleEvent( iter[i], pe, EventCpuCycles, sharedRingFd ) ) TracyDebug( " Target %i ok (EventCpuCycles)", i );
}
pe.config = PERF_COUNT_HW_INSTRUCTIONS;
for( int i=0; i<numIter; i++ )
{
if( OpenSampleEvent( iter[i], pe, EventInstructionsRetired ) ) TracyDebug( " Target %i ok (EventInstructionsRetired)", i );
if( OpenSampleEvent( iter[i], pe, EventInstructionsRetired, sharedRingFd ) ) TracyDebug( " Target %i ok (EventInstructionsRetired)", i );
}
}
@@ -1142,13 +1165,13 @@ bool SysTraceStart( int64_t& samplingPeriod )
}
for( int i=0; i<numIter; i++ )
{
if( OpenSampleEvent( iter[i], pe, EventCacheReference ) ) TracyDebug( " Target %i ok (EventCacheReference)", i );
if( OpenSampleEvent( iter[i], pe, EventCacheReference, sharedRingFd ) ) TracyDebug( " Target %i ok (EventCacheReference)", i );
}
pe.config = PERF_COUNT_HW_CACHE_MISSES;
for( int i=0; i<numIter; i++ )
{
if( OpenSampleEvent( iter[i], pe, EventCacheMiss ) ) TracyDebug( " Target %i ok (EventCacheMiss)", i );
if( OpenSampleEvent( iter[i], pe, EventCacheMiss, sharedRingFd ) ) TracyDebug( " Target %i ok (EventCacheMiss)", i );
}
}
@@ -1159,13 +1182,13 @@ bool SysTraceStart( int64_t& samplingPeriod )
ProbePreciseIp( pe, PERF_COUNT_HW_BRANCH_INSTRUCTIONS, PERF_COUNT_HW_BRANCH_MISSES, currentPid );
for( int i=0; i<numIter; i++ )
{
if( OpenSampleEvent( iter[i], pe, EventBranchRetired ) ) TracyDebug( " Target %i ok (EventBranchRetired)", i );
if( OpenSampleEvent( iter[i], pe, EventBranchRetired, sharedRingFd ) ) TracyDebug( " Target %i ok (EventBranchRetired)", i );
}
pe.config = PERF_COUNT_HW_BRANCH_MISSES;
for( int i=0; i<numIter; i++ )
{
if( OpenSampleEvent( iter[i], pe, EventBranchMiss ) ) TracyDebug( " Target %i ok (EventBranchMiss)", i );
if( OpenSampleEvent( iter[i], pe, EventBranchMiss, sharedRingFd ) ) TracyDebug( " Target %i ok (EventBranchMiss)", i );
}
}
@@ -1284,8 +1307,11 @@ bool SysTraceStart( int64_t& samplingPeriod )
tracy_free( iter );
tracy_free( sharedRingFd );
if( s_state.numBuffers == 0 || ( externalPid != 0 && s_state.ctxBufferIdx == 0 ) )
{
CloseRedirectFds();
tracy_free( s_state.ring );
s_state.ring = nullptr;
TracyDebug( "Failed to setup any system tracing events, system tracing disabled." );
@@ -1338,7 +1364,7 @@ static uint64_t* GetCallstackBlock( uint64_t cnt, RingBuffer& ring, uint64_t off
return trace;
}
void SysTraceWorker( void* ptr )
void SysTraceWorker( void* )
{
ThreadExitHandler threadExitHandler;
SetThreadName( "Tracy Sampling" );
@@ -1349,6 +1375,7 @@ void SysTraceWorker( void* ptr )
auto ringArray = s_state.ring;
auto numBuffers = s_state.numBuffers;
for( int i=0; i<numBuffers; i++ ) ringArray[i].Enable();
for( int i=0; i<s_state.numRedirectFd; i++ ) ioctl( s_state.redirectFd[i], PERF_EVENT_IOC_ENABLE, 0 );
for(;;)
{
#ifdef TRACY_ON_DEMAND
@@ -1730,6 +1757,7 @@ void SysTraceWorker( void* ptr )
}
for( int i=0; i<numBuffers; i++ ) ringArray[i].~RingBuffer();
CloseRedirectFds();
tracy_free_fast( ringArray );
}