Subject: Re: [PATCH net-next 1/5] selftests: drv-net: rss_ctx: fix cleanup in the basic test

From: Jakub Kicinski <[email-masked]>
Date: Mon, 8 Jul 2024 09:13:26 -0700

On Sat, 06 Jul 2024 09:53:41 -0400 Willem de Bruijn wrote:
> > @@ -89,6 +88,7 @@ from lib.py import ethtool, ip, defer, GenerateTraffic, CmdExitFailure
> >  
> >      # Set the indirection table
> >      ethtool(f"-X {cfg.ifname} equal 2")
> > +    reset_indir = defer(ethtool, f"-X {cfg.ifname} default")
> >      data = get_rss(cfg)
> >      ksft_eq(0, min(data['rss-indirection-table']))
> >      ksft_eq(1, max(data['rss-indirection-table']))
> > @@ -104,7 +104,7 @@ from lib.py import ethtool, ip, defer, GenerateTraffic, CmdExitFailure
> >      ksft_eq(sum(cnts[2:]), 0, "traffic on unused queues: " + str(cnts))
> >  
> >      # Restore, and check traffic gets spread again
> > -    ethtool(f"-X {cfg.ifname} default")
> > +    reset_indir.exec()  
> 
> When is this explicit exec needed?

When you want to run the cleanup _now_.

We construct the cleanup as soon as we allocate the resource,
it stays on the deferred list in case some exception makes us abort,
but the test may want to free the resource or reconfigure it further
as part of the test, in which case it can run .exec() (or cancel() to
discard the clean up without running it).

Here we do:
 1. constrain RSS
 2. run traffic (to check we're hitting expected queues)
 3. reset RSS
 4. run traffic (to check we're hitting all queues)

so step 3 runs the cleanup of step 1 explicitly.