linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Arnd Bergmann <arnd@arndb.de>
To: Ingo Molnar <mingo@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ard Biesheuvel <ardb@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Jonathan Corbet <corbet@lwn.net>
Subject: Re: [ANNOUNCE] "Fast Kernel Headers" Tree -v2
Date: Thu, 13 Jan 2022 10:20:22 +0100	[thread overview]
Message-ID: <CAK8P3a3FahVogb3wfbXSaCpnUsRBGmO9M56M+Cay=skc9rUzjw@mail.gmail.com> (raw)
In-Reply-To: <Yd/idffvv8QIQcEU@gmail.com>

On Thu, Jan 13, 2022 at 9:27 AM Ingo Molnar <mingo@kernel.org> wrote:
> * Arnd Bergmann <arnd@arndb.de> wrote:
> > On Mon, Jan 10, 2022 at 11:03 PM Arnd Bergmann <arnd@arndb.de> wrote:
> > > On Sat, Jan 8, 2022 at 5:26 PM Ingo Molnar <mingo@kernel.org> wrote:
> > > I've started building randconfig kernels for arm64 and x86, and fixing
> > > up things that come up, a few things I have noticed out so far:
> >
> > I have run into a couple more specific issues:
> >
> > * net/smc/smc_ib.c:824:26: error: implicit declaration of function
> > 'cache_line_size' [-Werror=implicit-function-declaration]
> > cache_line_size is generally provided by linux/cache.h, which includes
> > asm/cache.h.
> > This works on arm64, but not on x86, where asm/cache.h would have to include
> > asm/cpufeature.h, and but it would be good to avoid that because of the implicit
> > linux/percpu.h and linux/bitops.h inclusions. Also, if I add the
> > include, I get this
> > build failure instead: include/linux/smp_types.h:88:33: error:
> > requested alignment '20'
> > is not a positive power of 2
>
> Note that this particular one should be fixed in the WIP branch, which is
> at:
>
>    git://git.kernel.org/pub/scm/linux/kernel/git/mingo/tip.git sched/headers

Ok.

> > * arm64 has a couple of issues around asm/memory.h, linux/mm_types.h and
> > asm/page.h that can cause loops. I think my latest version has it figured
> > out, but there is probably room for optimization.
>
> Yeah, this is like the 5th attempt at finding a robust solution. :-/

It will likely come back in another form when more architectures get
converted then. I'm currently looking at reviving my own metrics scripts
from 2020 to see if I can improve arch/arm64 further, after that I was
planning to look at arch/arm/

> > * There is no general way to get the get_order() definition, other than
> > including asm/page.h from .c files. On arm64, this shows up in a couple
> > of files after the cleanup. Only xtensa and ia64 define their own version
> > of get_order(), and I think we should just remove those and move the
> > generic version to linux/getorder.h, where any file using it can pick it
> > up. For randconfig builds, I had to add asm/page.h to
> > net/xdp/xsk_queue.c, mm/memtest.c and
> > drivers/target/iscsi/iscsi_target_nego.c, after I removed the indirect
> > include from arch/arm64/include/asm/mmu.h in the previous step.
>
> Would including <linux/mm_page_address.h> be sufficient? That already has
> an <asm/page.h> inclusion and is vaguely related.

Sure, works for me.

> I tried to avoid as many low level headers as possible from the main types
> headers - and the get_order() functionality also brings in bitops
> definitions, which I'm still hoping to be able to reduce from its current
> ~95% utilization in a distro kernel ...

Agreed, I think reducing bitops.h and atomic.h usage is fairly important,
I think these are even bigger on arm64 than on x86.

> We could add <linux/page_api.h> as well, as a standardized header. We
> already have page_types.h and et_order() is a page types API.

More generally speaking, do you have a plan for how to document which
header to include for getting a particular symbol that is provided by
a header we don't want to include directly? I think iwyu has a particular
notation for it, but when I looked at using that in 2020 I decided it wouldn't
scale to the size of the kernel. I did my own shell script with a long
list of regex patterns, but I'm not convinced about that approach either.

       Arnd

  reply	other threads:[~2022-01-13  9:20 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-08 16:26 [ANNOUNCE] "Fast Kernel Headers" Tree -v2 Ingo Molnar
2022-01-10 22:03 ` Arnd Bergmann
2022-01-11 16:23   ` Arnd Bergmann
2022-01-11 17:08     ` David Laight
2022-01-13  8:27     ` Ingo Molnar
2022-01-13  9:20       ` Arnd Bergmann [this message]
2022-01-19 12:31         ` Ingo Molnar
2022-01-19 17:20           ` Arnd Bergmann
2022-01-22  9:18             ` Ingo Molnar
2022-01-13  8:57   ` Ingo Molnar
2022-01-13 10:16     ` Arnd Bergmann
2022-03-15 10:35 ` [TREE] "Fast Kernel Headers" Tree -v3 Ingo Molnar
2022-03-22  7:59   ` Kari Argillander
2022-03-22 15:37     ` Randy Dunlap
2022-03-22 16:22       ` Kari Argillander
2022-03-22 19:03         ` Kari Argillander
2023-11-04  9:07           ` Lucas Tanure

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAK8P3a3FahVogb3wfbXSaCpnUsRBGmO9M56M+Cay=skc9rUzjw@mail.gmail.com' \
    --to=arnd@arndb.de \
    --cc=akpm@linux-foundation.org \
    --cc=ardb@kernel.org \
    --cc=corbet@lwn.net \
    --cc=gregkh@linuxfoundation.org \
    --cc=jpoimboe@redhat.com \
    --cc=linux-arch@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=nathan@kernel.org \
    --cc=peterz@infradead.org \
    --cc=torvalds@linux-foundation.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).