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@vepadulano : thanks for reporting the outcome of your tests! could you just tell me which version of xrdcp you were using?
To shed some light on your results:
XRD_PARALLELEVTLOOP is by default set to 1, and is the number of event-loop threads handling the async I/O; in some cases e.g. if the xrootd client is interacting with many servers (as it does in case of XCache) a single event loop can become CPU bound and in those scenarios it makes sense to use multiple event-loops
XRD_WORKERTHREADS is by default set to 3, and is the number of threads in the thread-pool used to call user completion handlers
The two variables seem to be independently adding threads to the xrdcp process when they are increased.
Your observation is correct, those two variable are responsible for totally independent pool of threads.
there is also the TaskManager thread, which runs various timers, amongst others responsible for the request timeouts
in case of xrdcp there is also the main execution thread
To summarise, in case of xrdcp if one sets XRD_PARALLELEVTLOOP=1 and XRD_WORKERTHREADS=1 there should be 4 threads, which is what I observe in my xrdcp process:
(gdb) info threads
Id Target Id Frame
4 Thread 0x7ffff1224700 (LWP 17480) "xrdcp" 0x00007ffff644bb3b in do_futex_wait.constprop.1 () from /lib64/libpthread.so.0
3 Thread 0x7ffff1a25700 (LWP 17479) "xrdcp" 0x00007ffff69368ed in nanosleep () from /lib64/libc.so.6
2 Thread 0x7ffff2226700 (LWP 17478) "xrdcp" 0x00007ffff696ffd3 in epoll_wait () from /lib64/libc.so.6
* 1 Thread 0x7ffff7fb3900 (LWP 17465) "xrdcp" XrdCl::ClassicCopyJob::Run (this=0x66e960, progress=0x7fffffffca50) at /home/simonm/git/xrootd/src/XrdCl/XrdClClassicCopyJob.cc:2400
[simonm@idefix ~]$ ps -elf | grep xrdcp
0 S simonm 17453 1021 0 80 0 - 86484 poll_s 13:58 pts/0 00:00:01 gdb ./xrdcp
0 t simonm 17465 17453 0 80 0 - 62609 ptrace 13:59 pts/0 00:00:00 /home/simonm/git/xrootd/build/src/XrdCl/./xrdcp -f Makefile root://slc7-test//tmp
[simonm@idefix ~]$ ps hH p 17465 | wc -l
4
Now I'm not sure where is this one additional thread you are seeing coming from, that's why I asked about the version you are using.
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