On Thu, Oct 26, 2023 at 11:35 PM Arnd Bergmann [off-list ref] wrote:

On Fri, Oct 27, 2023, at 01:54, Kent Overstreet wrote:

quoted

On Fri, Oct 27, 2023 at 01:05:48AM +0200, Thomas Gleixner wrote:

quoted

On Thu, Oct 26 2023 at 18:33, Suren Baghdasaryan wrote:

quoted

On Wed, Oct 25, 2023 at 5:33 PM Thomas Gleixner [off-list ref] wrote:

quoted

quoted

This avoids a circular header dependency in an upcoming patch by only
making hrtimer.h depend on percpu-defs.h

What's the actual dependency problem?

Sorry for the delay.
When we instrument per-cpu allocations in [1] we need to include
sched.h in percpu.h to be able to use alloc_tag_save(). sched.h

Including sched.h in percpu.h is fundamentally wrong as sched.h is the
initial place of all header recursions.

There is a reason why a lot of funtionalitiy has been split out of
sched.h into seperate headers over time in order to avoid that.

Yeah, it's definitely unfortunate. The issue here is that
alloc_tag_save() needs task_struct - we have to pull that in for
alloc_tag_save() to be inline, which we really want.

What if we moved task_struct to its own dedicated header? That might be
good to do anyways...

Yes, I agree that is the best way to handle it. I've prototyped
a more thorough header cleanup with good results (much improved
build speed) in the past, and most of the work to get there is
to seperate out structures like task_struct, mm_struct, net_device,
etc into headers that only depend on the embedded structure
definitions without needing all the inline functions associated
with them.

This is something I'll add to our automation todos which I plan to
talk about at plumbers; I feel like it should be possible to write a
script that given a header and identifier can split whatever
declaration out into a new header, update the old header, then add the
necessary includes for the newly created header to each dependent
(optional).
-- 
Thanks,
~Nick Desaulniers