Re: [Ksummit-discuss] [MAINTAINERS SUMMIT] & [TECH TOPIC] Improve regression tracking

On Wed, 5 Jul 2017 16:06:07 +0200
Greg KH [off-list ref] wrote:

On Wed, Jul 05, 2017 at 09:27:57AM -0400, Steven Rostedt wrote:

quoted

Your "b" above is what I would like to push. But who's going to enforce
this? With 10,000 changes per release, and a lot of them are fixes, the
best we can do is the honor system. Start shaming people that don't
have a regression test along with a Fixes tag (but we don't want people
to fix bugs without adding that tag either). There is a fine line one
must walk between getting people to change their approaches to bugs and
regression tests, and pissing them off where they start doing the
opposite of what would be best for the community.  

I would bet, for the huge majority of our fixes, they are fixes for
specific hardware, or workarounds for specific hardware issues.  Now
writing tests for those is not an impossible task (look at what the i915
developers have), but it is very very hard overall, especially if the
base infrastructure isn't there to do it.

For specific examples, here's the shortlog for fixes that went into
drivers/usb/host/ for 4.12 after 4.12-rc1 came out.  Do you know of a
way to write a test for these types of things?
	usb: xhci: ASMedia ASM1042A chipset need shorts TX quirk
	usb: xhci: Fix USB 3.1 supported protocol parsing
	usb: host: xhci-plat: propagate return value of platform_get_irq()
	xhci: Fix command ring stop regression in 4.11
	xhci: remove GFP_DMA flag from allocation
	USB: xhci: fix lock-inversion problem
	usb: host: xhci-ring: don't need to clear interrupt pending for MSI enabled hcd
	usb: host: xhci-mem: allocate zeroed Scratchpad Buffer
	xhci: apply PME_STUCK_QUIRK and MISSING_CAS quirk for Denverton
	usb: xhci: trace URB before giving it back instead of after
	USB: host: xhci: use max-port define
	USB: ehci-platform: fix companion-device leak
	usb: r8a66597-hcd: select a different endpoint on timeout
	usb: r8a66597-hcd: decrease timeout

And look at the commits with the "Fixes:" tag in it, I do, I read every
one of them.  See if writing a test for the majority of them would even
be possible...

I don't mean to poo-poo the idea, but please realize that around 75% of
the kernel is hardware/arch support, so that means that 75% of the
changes/fixes deal with hardware things (yes, change is in direct
correlation to size of the codebase in the tree, strange but true).

I would say that if it's for a specific hardware, then it's really up
to the maintainer if there should be a test or not. As a lot of these
is just to deal with some quirk or non standard that the hardware does.
But are these regressions, or just some feature that's been broken on
that hardware since its conception?

That is, Thorsten this is more for you, how much real regressions are in
hardware? A bug that's been there forever is not a regression. It's a
feature ;-)  A regression is something that use to work and now does
not. Is that number still as high with hardware? Those probably could
be where tests can be focused on.

I'm worried more about infrastructure too. I would look at general
functionality of say USB, to see if something can be written to test a
device. Using the one change above that actually mentions "regression"
would it be possible to test completion codes? (I have no idea, I only
read the change log and I'm speaking out of my derrière)

If we have a bunch of generic tests that can test hardware (general
video tests, USB tests, network cards, etc) and people ran these on
their own hardware, and it were to trigger a failure, then it would be
easier for users to report these issues to the maintainers. And these
would be easier to find and fix.

No test should be written for a single specific hardware. It should be a
general functionality that different hardware can execute.

If only I had a subsystem that didn't have to deal with hardware, that
must be so easy to work with :)

*smack*!  ;-)

-- Steve