Re: [PATCH v3 18/19] x86/resctrl: Add cpu offline callback for resctrl work

Ilpo Järvinen
2023-04-27T14:52:00Z

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On Thu, 27 Apr 2023, James Morse wrote:

> Hi Ilpo,
>
> On 21/03/2023 15:32, Ilpo Järvinen wrote:
> > On Mon, 20 Mar 2023, James Morse wrote:
> >
> >> The resctrl architecture specific code may need to free a domain when
> >> a CPU goes offline, it also needs to reset the CPUs PQR_ASSOC register.
> >> The resctrl filesystem code needs to move the overflow and limbo work
> >> to run on a different CPU, and clear this CPU from the cpu_mask of
> >> control and monitor groups.
> >>
> >> Currently this is all done in core.c and called from
> >> resctrl_offline_cpu(), making the split between architecture and
> >> filesystem code unclear.
> >>
> >> Move the filesystem work into a filesystem helper called
> >> resctrl_offline_cpu(), and rename the one in core.c
> >> resctrl_arch_offline_cpu().
> >>
> >> The rdtgroup_mutex is unlocked and locked again in the call in
> >> preparation for changing the locking rules for the architecture
> >> code.
> >>
> >> resctrl_offline_cpu() is called before any of the resource/domains
> >> are updated, and makes use of the exclude_cpu feature that was
> >> previously added.
>
> >> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> >> index aafe4b74587c..4e5fc89dab6d 100644
> >> --- a/arch/x86/kernel/cpu/resctrl/core.c
> >> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> >> @@ -578,22 +578,6 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
> >>
> >> return;
> >> }
> >> -
> >> - if (r == &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl) {
> >> - if (is_mbm_enabled() && cpu == d->mbm_work_cpu) {
> >> - cancel_delayed_work(&d->mbm_over);
> >> - /*
> >> - * exclude_cpu=-1 as this CPU has already been removed
> >> - * by cpumask_clear_cpu()d
> >> - */
> >
> > This was added in 17/19 and now removed (not moved) in 18/19. Please avoid
> > such back-and-forth churn.
>
> This is the cost of making small incremental changes that should be easier to review.
> The intermediate step was a little odd, so came with a comment. (I normally mark those as
> 'temporary', but didn't bother this time as they are adjacent patches)

Why not mention the oddity at the end of changelog then? That keeps the
diffs clean of temporary comments.

> If you'd prefer, I can merge these patches together... but from
> Reinette's feedback its likely I'll split them up even more.

I don't prefer merging.

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i.