Re: First kernel patch (optimization)

From: Raymond Jennings
Date: Fri Sep 18 2015 - 05:31:36 EST

On 09/18/15 00:42, Greg KH wrote:
On Thu, Sep 17, 2015 at 11:12:51PM -0400, Theodore Ts'o wrote:
On Wed, Sep 16, 2015 at 01:26:51PM -0400, Josh Boyer wrote:
That isn't true. It helps the submitter understand the workflow and
expectations. What you meant to say is that it doesn't help you.
The problem is that workflow isn't the hard part. It's the part that
can be taught most easily, sure. But people seem to get really hung
up on it, and I fear that we have people who never progress beyond
sending trivial patches and spelling fixes and white space fixes and
micro-optimizations.

If the "you too can be a kernel developer" classes and web sites and
tutorials also taught people how to take performance measurements, and
something about the scientific measurement, that would be something.
Or if it taught people how to create tests and to run regression
testing. Or if it taught people how to try to do fuzz testing, and
then once they find a sequence which causes crash, how to narrow down
the failure to a specific part of the kernel, and how to fix and
confirm that the kernel no longer crashes with the fix --- that would
be useful.

If they can understand kernel code; if they can understand the
scientific measurement; if they can understand how to do performance
measurements --- being able to properly format patches is something
which most kernel developers can very easily guide a new contributor
to do correctly. Or in the worst case, it doesn't take much time for
me to fix a whitespace problem and just tell the contributor --- by
the way, I fixed up this minor issue; could you please make sure you
do this in the future?

But if a test hasn't been tested, or if the contributor things it's a
micro-optimization, but it actually takes more CPU time and/or more
stack space and/or bloats the kernel --- that's much more work for the
kernel maintainer to have to deal with when reviewing a patch.

So I have a very strong disagreement with the belief that teaching
people the workflow is the more important thing. In my mind, that's
like first focusing on the proper how to properly fill out a golf
score card, and the ettiquette and traditions around handicaps, etc
--- before making sure the prospective player is good at putting and
driving. Personally, I'm terrible at putting and driving, so spending
a lot of time learning how to fill out a golf score card would be a
waste of my time.

A good kernel programmer has to understand systems thinking; how to
figure out abstractions and when it's a good thing to add a new layer
of abstraction and when it's better to rework an exsting abstraction
layer.

If we have someone who knows the workflow, but which doesn't
understand systems thinking, or how to do testing, then what? Great,
we've just created another Nick Krause. Do you think encouraging a
Nick Krause helps anyone?

If people really are hung up on learning the workflow, I don't mind if
they want to learn that part and send some silly micro-optimization or
spelling fix or whitespace fix. But it's really, really important
that they move beyond that. And if they aren't capable of moving
beyond that, trying to inflate are recruitment numbers by encouraging
someone who can only do trivial fixes means that we may be get what we
can easily measure --- but it may not be what we really need as a
community.
Ted, you are full of crap.

Where do you think that "new developers" come from? Do they show up in
our inbox, with full knowledge of kernel internals and OS theory yet
they somehow just can't grasp how to submit a patch correctly? Yes,
they sometimes rarely do. But for the majority of people who got into
Linux, that is not the case at all.

People need to start with something simple, and easy, to get over the
hurdles of:
- generating a patch
- sending an email
- fixing the email client as it just corrupted the patch
- fix the subject line as it was incorrect
- fix the changelog as it was missing
- fix the email client again as it corrupted the patch in a
different way
- giving up on using a web email client as it just will not work
- figuring out who to send the patch to
- fixing the email client as the mailing list bounced the email

Those are non-trivial tasks. And by starting with "remove this space"
you take the worry away from the specific content of the patch, and let
them worry about the "hard" part first.
+1 for this.

For example, I for one cannot tell you how many times gmail snuck html sections into my outgoing emails before I finally caught it red handed and switched to using a local native client.

Then, after all of the above is finished, and working, then they can
start submitting real patches, that do real things, in patch series, as
they can focus on the content much more, as the problems of how to make
the patch into an acceptable format is not an issue anymore.

Did anyone read linus torvald's post that I linked to earlier?

It was very much relevant to the present situation and covers something like this that happened before with a newbie developer.

I see this every single day with patches in the staging tree, which is
why it is there, and is why I don't just go and remove all coding style
errors in one fell-swoop tomorrow. We need to provide those "simple"
tasks to get people involved in our community and over the hurdle of
sending a patch in.

And from there, then people go on to contribute "real" things. There
are _many_ subsystem maintainers that started out submitting whitespace
patches. There are even more developers who have gotten "real" jobs by
starting out submitting whitespace patches and personally I find that a
much more satisfying metric than more subsystem maintainers.

Yes, not everyone who sends in cleanup patches will go on to be a
maintainer, or get a job, but the thing is, you can't judge who will, or
will not, be that person. What we have to do, and what we must do, is
accept everyone into our community as somewhere, someone is out there
that you will want to take over for your subsystem when you are tired of
it. And by turning away people from doing things to get over our first
hurdles by adding to it by forcing someone to make a "real"
contribution, you just lost that person forever.

So don't take cleanup patches for your code, that's fine, and I totally
understand why _you_ don't want to do that. But to blow off the effort
as being somehow trivial and not worthy of us, that's totally missing
the point, and making things harder on yourself in the end.

Just point people at staging, that's what it is there for, and is what
I, and the developers who help maintain it, do every single day because
we know it is essential for the future of Linux to do so.

And if they don't move on beyond whitespace cleanups, that's fine too,
I'll still gladly take those patches, and do so. But almost always the
person moves from that into doing something "real" or they tire of it
and stop contributing. By somehow pre-rejecting these people, you are
pre-judging them as well, a _VERY_ dangerous thing to do to anyone.

Do you know what _my_ first email was to lkml all those years ago? "How
do you make a patch in the proper format?" And I asked it because I saw
a "trivial" change that I was able to make. And do you know who
answered that question? Someone who ended up being my manager for many
years, and now runs SuSE Labs. He was wise enough to take the time to
help a "newbie" like myself because he knew that we all started
somewhere, and that we never know just who that "newbie" might turn out
to be in the end.

So don't be a jerk, and spout off as to how we only need "skilled"
people contributing. Of course we need that, but the way we get those
people is to help them become skilled, not requiring them to show up
with those skills automatically.

greg k-h
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