[LU-7195] Allow for static string content for jobstats jobid_var

Related — Thu, 2 Feb 2017 16:56:24 +0000

We've been benchmarking I/O performance (mainly metadata operations) with job stats enabled. There's potential for a performance impact when using the environment variable setup. This performance degradation appears to be associated with the environment variable lookup. The impact when using the special procname_uid setting is negligible.

To counter this, we would like to see the ability to support a static string that's not evaluated as an environment variable, but is simply passed along with the rpc.

I would like to propose using a prefix to the jobid_var variable to indicate that it should be passed, not evaluated. I think it would make sense to use a symbol like @ for this prefix. I'm basing this on my assumption that environment variables compliant with IEEE Std 1003.1-2001 will not contain the at-sign. This would allow administrators to statically set this at a job start, or using the client's hostname, etc, without the overhead of the environment lookup. This also allows us the ability to take this out of the user's control without resorting to read-only variables in their environments.

Examples of use:

Associating traffic per-host: lctl set_param jobid_var="@$(hostname)"

Associating traffic with a specific string: lctl set_param jobid_var="@benchmarking"

From my understanding, it looks like this would be a pretty straight forward change to the obd class, within the lustre_get_jobid function. I have a potential patch I can push to master if this is a behavior we want supported.

Thanks!
–
Jesse

Whamcloud Community JIRA

[LU-7195] Allow for static string content for jobstats jobid_var