Directory overrides for Profiling with +JPperf true

[flamble]

Is your feature request related to a problem? Please describe.
When using +JPperf true two types of file are created in /tmp. I would like to be able to place the files in a directory of my choice. The motivation is so that I can put them on a different mount from /tmp.

1. jit-<pid>.dump
   

   otp/erts/emulator/beam/jit/beam_jit_metadata.cpp

   Lines 328 to 333 in 4929103

   	char name[MAXPATHLEN];
   	FileHeader header;
   	/* LLVM places this file in ~/.debug/jit/ maybe we should do that to? */
   	erts_snprintf(name, sizeof(name), "/tmp/jit-%d.dump", getpid());

2. perf-<pid>.map
   

   otp/erts/emulator/beam/jit/beam_jit_metadata.cpp

   Lines 469 to 475 in 4929103

   	char name[MAXPATHLEN];
   	size_t namesz = sizeof(name);
   	if (erts_sys_explicit_host_getenv("ERL_SYM_MAP_FILE", name, &namesz) !=
   	1) {
   	snprintf(name, sizeof(name), "/tmp/perf-%i.map", getpid());
   	}

You can already use ERL_SYM_MAP_FILE to override the map filename (not just the directory):

• No such override is there for the jit files
• It would be useful if the existing filenames could be used, but an override could place the files in a different directory.

Describe the solution you'd like

For both types of file, the ability to override the directory. Using the jit file as an example:

        char* dirName;
        if (!(dirName = getenv("ERL_PERF_DIR"))) {
            dirName = "/tmp";
        }

        erts_snprintf(name, sizeof(name), "%s/jit-%d.dump", dirName, getpid());

Describe alternatives you've considered

• Same variable name for both or individual variables for each file type
• Making use of more standard variables like TMP/TMPDIR

Additional context

Please let me know if you'd prefer to solve this another way, or if there's a preference/guidelines you follow with environment variable usage/naming. I am happy to test + PR this once the naming/suggestion is agreed. Thanks!

[garazdawi]

Hello!

In general we do not want to use environment variables for configurting how erts should run, so it would be bettere if this is a command line option. I think +JPperfdirectory <directory> is a good enough name :) A PR adding it + docs + tests would be welcome.

We used the environment variable ERL_SYM_MAP_FILE because it is an internal API only to be used by cerl.

[flamble]

Thanks @garazdawi - I'll make a change as suggested, with +JPperfdirectory <directory>.

We used the environment variable ERL_SYM_MAP_FILE because it is an internal API only to be used by cerl.

makes sense!