how to open the GCLog ？

[shushanhf]

Hi, @Maoni0
How to open the GCLog ?
For example the runtime6.0,
I modify the src/coreclr/gc/gcconfig.h

+    BOOL_CONFIG  (LogEnabled,             "GCLogEnabled",           NULL,                             true,             "Specifies if you want to turn on logging in GC")  

Also open the macros within the gc/gcpriv.h

+#define TRACE_GC
+#define SIMPLE_DPRINTF

export DOTNET_GCLogEnabled=1
export DOTNET_GCLogFileSize=100
export DOTNET_GCLogFile="/home/qiao/GCLogQiao.log"
export DOTNET_StressLog=0
#export DOTNET_gcConcurrent=0
#export DOTNET_GCName="libclrgc.so"
export DOTNET_GCRegionsRange=20000000
export DOTNET_heapverify=1

But the created file /home/qiao/GCLogQiao.log.log is empty.

[Maoni0]

you'll need to enable logging in the code first - uncomment these 2 lines in gcpriv.h -

#define TRACE_GC
#define SIMPLE_DPRINTF

this is not compiled in by default because this is the internal GC log and is mostly only meant to be used for active GC development.

[shushanhf]

Sorry, I did't get it.
After uncomment the two lines

#define TRACE_GC
#define SIMPLE_DPRINTF

Which env value should be opened ? The export DOTNET_GCLogEnabled=1 or the DOTNET_LogEnable=1 and DOTNET_LogToConsole=1 ?
But the last two are not the GC's info.

[Maoni0]

you had them already -

export DOTNET_GCLogEnabled=1
export DOTNET_GCLogFileSize=100
export DOTNET_GCLogFile="/home/qiao/GCLogQiao.log"
export DOTNET_StressLog=0

[shushanhf]

Thanks.
But there is no /home/qiao/GCLogQiao.log.log created after these values opened.

Liking these lines
https://github.com/dotnet/runtime/blob/4a336b1c4756fe95274658c15bc9a4674625a8b2/src/coreclr/gc/gc.cpp#L12493-L12499

The macro #ifdef TRACE_GC is not defined. The GCLogFile will not be created.

[Maoni0]

you mean TRACE_GC is not defined?
it should be defined in gcpriv.h if you uncomment those 2 lines I mentioned above.

[shushanhf]

But if defined the TRACE_GC, the file /home/qiao/GCLogQiao.log.log is created only as an empty log file.

[Maoni0]

you need to define TRACE_GC or the code to create a log wouldn't be there. this is what I shared with another customer who needed to get the dprintf logs: trace_gc. this enables logging code and shows how to change the level so you can log just the selected few things.

have you done any GCs? if not, the log is still in memory. we always flush the in-memory buffer to the file in do_post_gc (see flush_gc_log (false);). make sure you are actually doing GCs. if you want to see what's in the in-memory buffer, you can dump what's at WKS::gc_log_buffer (current offset is WKS::gc_log_buffer_offset). replace WKS with SVR if you are using Server GC. see the (simple) implementation in log_va_msg. I would suggest to do a little debugging if this doesn't work.