Re: [PATCH v3 1/2] x86/resctrl: Pass domain to target CPU

Reinette Chatre
2024-02-27T22:05:18Z

Hi Tony,

On 2/22/2024 10:50 AM, Tony Luck wrote:
> reset_all_ctrls() and resctrl_arch_update_domains() use on_each_cpu_mask()
> to call rdt_ctrl_update() on potentially one CPU from each domain.
>
> But this means rdt_ctrl_update() needs to figure out which domain to apply
> changes to. Doing so requires a search of all domains in a resource,
> which can only be done safely if cpus_lock is held. Both callers do
> hold this lock, but there isn't a way for a function called on another
> CPU via IPI to verify this.
>
> Commit c0d848fcb09d ("x86/resctrl: Remove lockdep annotation that triggers
> false positive") removed the incorrect assertions.
>
> Adding the target domain to the msr_param structure, and calling
> for each domain separately using smp_call_function_single() means
> that rdt_ctrl_update() doesn't need to search for the domain. Thus
> get_domain_from_cpu() can safely assert that the cpus_lock is held since
> the remaining callers do not use IPI.

Please stick to the imperative tone. Something like (please feel free to
improve):

Add the target domain to the msr_param structure and call
rdt_ctrl_update() for each domain separately using
smp_call_function_single(). This means that rdt_ctrl_update()
doesn't need to search for the domain and get_domain_from_cpu()
can safely assert that the cpus_lock is held since
the remaining callers do not use IPI.

...

> @@ -463,6 +457,8 @@ static int domain_setup_ctrlval(struct rdt_resource *r, struct rdt_domain *d)
> hw_dom->ctrl_val = dc;
> setup_default_ctrlval(r, dc);
>
> + m.res = r;

This belongs in the next patch.

> + m.dom = d;
> m.low = 0;
> m.high = hw_res->num_closid;
> hw_res->msr_update(d, &m, r);

The rest looks good to me and I think it is a good improvement.
Thank you very much.

Reinette