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

James Morse
2023-04-27T14:21:36Z

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)

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

Thanks,

James