Re: [GIT PULL] Second set of RISC-V updates for v5.5-rc1

[Alistair Francis <Alistair.Francis@wdc.com>]

On Thu, 2019-12-05 at 15:29 -0800, Alistair Francis wrote:
> On Thu, 2019-12-05 at 15:12 -0800, Paul Walmsley wrote:
> > On Thu, 5 Dec 2019, Alistair Francis wrote:
> > 
> > > On Wed, 2019-12-04 at 18:54 -0800, Paul Walmsley wrote:
> > > > On Wed, 4 Dec 2019, Alistair Francis wrote:
> > > > 
> > > > > It is too much to expect every distro to maintain a defconfig
> > > > > for 
> > > > > RISC-V.
> > > > 
> > > > The major Linux distributions maintain their own kernel
> > > > configuration 
> > > > files, completely ignoring kernel defconfigs.  This has been so
> > > > for a 
> > > > long time.
> > > 
> > > That might be true for the traditional "desktop" distros, but
> > > embedded
> > > distros (the main target for RISC-V at the moment) don't
> > > generally
> > > do
> > > this.
> > 
> > Maybe in this discussion we can agree to use the common
> > distinction 
> > between distributions and distribution build frameworks, where
> > users
> > of 
> > the latter need to be more technically sophisticated - as opposed
> > to 
> > downloading a disk image.
> 
> Why is there a distinction?
> 
> There are lots of disk images that you can just download which are
> based on OE or buildroot. Lots of people use OE images and never
> realise it.
> 
> In the same way that there are build enviroments based on the
> standard
> "desktop" distros. In both cases these are distros.
> 
> > > > > Which is why we currently use the defconfig as a base and
> > > > > apply 
> > > > > extra features that distro want on top.
> > > > 
> > > > As you know, since you've worked on some of the distribution
> > > > builder 
> > > > frameworks (not distributions) like OE and Buildroot, those
> > > > build 
> > > > systems have sophisticated kernel configuration patching and
> > > > override 
> > > > systems that can disable the debug options if the maintainers
> > > > think 
> > > > it's a good idea to do that.
> > > 
> > > Yes they do. As I said, we start with the defconfig and then
> > > apply
> > > config changes on top. Every diversion is a maintainence burden
> > > so
> > > where possible we don't make any changed. All of the QEMU
> > > machines
> > > currently don't have config changes (and hopefully never will) as
> > > it's
> > > a pain to maintain.
> > 
> > I'm open to your concerns here.  Can you help me understand why
> > adding a 
> > few lines to the kernel configuration fragments to disable the
> > debug 
> > options creates maintenance pain?  Isn't it just a matter of adding
> > a
> 
> For one, we have the same burden as you do.
> 
> You feel that it's too much of a burden to have a config fragment in
> tree to enable debug. You clearly feel that having a
> `extra_debug.config` fragment for you is too much of a burden, why is
> it not a burden for distros?
> 
> > few 
> > lines to disable the debug options, and -- since you clearly don't
> > want 
> > them enabled for any platform -- just leaving them in there?
> 
> Leave them in where?
> 
> No other architecture does this. Now we have to have a special config
> fragment added just for RISC-V. Why is RISC-V so special that it
> needs
> it's own fragment that other arches don't have?
> 
> > > > > > distros and benchmarkers will create their own Kconfigs for
> > > > > > their
> > > > > > needs.
> > > > > 
> > > > > Like I said, that isn't true. After this patch is applied
> > > > > (and
> > > > > it 
> > > > > makes it to a release) all OE users will now have a slower
> > > > > RISC-V 
> > > > > kernel.
> > > > 
> > > > OE doesn't have any RISC-V support upstream, so pure OE users
> > > > won't
> > > > notice 
> > > 
> > > That is just not true. 
> > 
> > After getting your response, I reviewed the OE-core tree that I
> > have
> > here, 
> > which is based on following the OE-core "getting started"
> > instructions. 
> > The result is a tree with no RISC-V machine support.  Looking again
> > at 
> > those instructions, I see that they check out the last release,
> > rather 
> > than the current top of the tree; and the current top of tree does
> > have a 
> > QEMU RISC-V machine.  So this statement of yours is correct, and I
> > was in 
> > error about the current top-of-tree OE-core support.
> 
> The last release (Zeus) also has RISC-V support....

Whoops, I left the dots to remind me to come back and double check
this, but then I forgot to remove them.

> 
> > > You talk later about misinformation but this is a blatent lie.
> > 
> > This isn't acceptable.  We've met each other in person, and I've 
> > considered you an enjoyable and trustworthy person to discuss
> > technical 
> > issues with.  This is the first time that you've ever publicly
> > accused me 
> > of misrepresenting an issue with intent to deceive.  There's a big 
> > difference between stating that someone is quoting misinformation
> > and 
> > accusing someone of bad intentions.  I expect an apology from you.
> 
> I didn't say you had bad intentions. I was just pointing out that you
> spent the time researching points that match your argument, but
> didn't
> check to see what current RISC-V support is.
> 
> I don't see a difference between saying someone is spreading
> misinformation and lying, but I am sorry if it upset you.

Just to clarify, I am sorry that I upset you. I did not mean to do
that.

I do not appriate you saying that I am spreading misinformation,
espicially when there are numbers to back up the claim of slowing down
defconfig users.

Alistair

> 
> > > > > Slowing down all users to help kernel developers debug seems
> > > > > like 
> > > > > the wrong direction. Kernel developers should know enough to
> > > > > be
> > > > > able 
> > > > > to turn on the required configs, why does this need to be
> > > > > the 
> > > > > default?
> > > > 
> > > > It's clear you strongly disagree with the decision to do
> > > > this.  It's 
> > > > certainly your right to do so.  But it's not good to spread 
> > > > misinformation about how changing the defconfigs "slow[s] down
> > > > all 
> > > > users," or
> > > 
> > > What misinformation?
> 
> Somehow it looks like you dropped this paragraph from my response,
> I'll
> just add it back in:
> 
> ******
> Anup shared benchmarking results indicating that this change has a
> 12%
> performance decrease for everyone who uses the defconfig without
> removing this change.
> ******
> 
> > You've already acknowledged in your response that the major Linux 
> > distributions don't use defconfigs.  So it's clear that your 
> 
> What do you mean major?
> 
> AFAIK OE and buildroot are the only distros that have first class
> RISC-
> V support. That seems pretty major to me.
> 
> > statement is 
> > false, and rather than admitting that you're wrong, you're doubling
> > down.
> 
> Doubling down on what? I never claimed all distros use defconfigs.
> 
> > > > exaggerating the difficulty for downstream software
> > > > environments
> > > > to 
> > > > back this change out if they wish.
> > > 
> > > If you think it is that easy can you please submit the patches?
> > 
> > For my part, I'd be happy if the current RISC-V OE and Buildroot
> > users who 
> > don't change the kernel configs run with the defconfig debug
> > options 
> > enabled right now.   So, I don't plan to send patches for them.
> 
> That is what will continue to happen. All users will be expected to
> live with a 12% performance impact.
> 
> > > I understand it's easy to make decisions that simplfy your flow,
> > > but
> > > this has real negative consequences in terms of performance for
> > > users
> > > or complexity for maintainers. It would be nice if you take other
> > > users
> > > /developers into account before merging changes.
> > 
> > As stated earlier, I'm open to reconsidering if it indeed is
> > onerous,
> > and 
> > not just a matter of patching a few lines of kernel configuration 
> > fragments in OE and Buildroot once.
> 
> I don't understand, if patching a config is so easy why not just have
> a
> fragment in the kernel tree and you can use that when you build a
> kernel? This is what Daniel Thompson pointed out. That would avoid
> this
> issue and have it easy for you to build a kernel with debug support.
> How is that not the best solution?
> 
> AFIAK no other architecture has all these debug options enabled in
> the
> defconfi, why is RISC-V so special?
> 
> Alistair
> 
> > 
> > - Paul