Re: [PATCH v10 06/10] fs/resctrl: Add user interface to enable/disable io_alloc feature

[Babu Moger]

Hi Reinette,

Thanks for the review.

On 10/24/25 18:43, Reinette Chatre wrote:
> Hi Babu,
>
> On 10/21/25 4:54 PM, Babu Moger wrote:
>
> ...
>
> > When resctrl is mounted with "-o cdp" to enable code/data prioritization,
> > there are two L3 resources that can support I/O allocation: L3CODE and
> > L3DATA.  From resctrl fs perspective the two resources share a CLOSID and
> > the architecture's available CLOSID are halved to support this.  The
> > architecture's underlying CLOSID used by SDCIAE when CDP is enabled is the
> > CLOSID associated with the CDP_CODE resource, but from resctrl's perspective
> > there is only one CLOSID for both CDP_CODE and CDP_DATA. CDP_DATA is thus
> > not usable for general (CPU) cache allocation nor I/O allocation. Keep the
> > CDP_CODE and CDP_DATA I/O alloc status in sync to avoid any confusion to
> > user space. That is, enabling io_alloc on CDP_CODE does so on CDP_DATA and
> > vice-versa, and keep the I/O allocation CBMs of CDP_CODE and CDP_3DATA in
> > sync.
> CDP_3DATA -> CDP_DATA

Sure.


> ...
>
> > +ssize_t resctrl_io_alloc_write(struct kernfs_open_file *of, char *buf,
> > +			       size_t nbytes, loff_t off)
> > +{
> > +	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
> > +	struct rdt_resource *r = s->res;
> > +	char const *grp_name;
> > +	u32 io_alloc_closid;
> > +	bool enable;
> > +	int ret;
> > +
> > +	ret = kstrtobool(buf, &enable);
> > +	if (ret)
> > +		return ret;
> > +
> > +	cpus_read_lock();
> > +	mutex_lock(&rdtgroup_mutex);
> > +
> > +	rdt_last_cmd_clear();
> > +
> > +	if (!r->cache.io_alloc_capable) {
> > +		rdt_last_cmd_printf("io_alloc is not supported on %s\n", s->name);
> > +		ret = -ENODEV;
> > +		goto out_unlock;
> > +	}
> > +
> > +	/* If the feature is already up to date, no action is needed. */
> > +	if (resctrl_arch_get_io_alloc_enabled(r) == enable)
> > +		goto out_unlock;
> > +
> > +	io_alloc_closid = resctrl_io_alloc_closid(r);
> > +	if (!resctrl_io_alloc_closid_supported(io_alloc_closid)) {
> > +		rdt_last_cmd_printf("io_alloc CLOSID (ctrl_hw_id) %u is not available\n",
> > +				    io_alloc_closid);
> > +		ret = -EINVAL;
> > +		goto out_unlock;
> > +	}
> > +
> > +	if (enable) {
> > +		if (!closid_alloc_fixed(io_alloc_closid)) {
> > +			grp_name = rdtgroup_name_by_closid(io_alloc_closid);
> > +			WARN_ON_ONCE(!grp_name);
> > +			rdt_last_cmd_printf("CLOSID (ctrl_hw_id) %u for io_alloc is used by %s group\n",
> > +					    io_alloc_closid, grp_name ? grp_name : "another");
> > +			ret = -ENOSPC;
> > +			goto out_unlock;
> > +		}
> > +
> > +		ret = resctrl_io_alloc_init_cbm(s, io_alloc_closid);
> > +		if (ret) {
> > +			rdt_last_cmd_puts("Failed to initialize io_alloc allocations\n");
> > +			closid_free(io_alloc_closid);
> > +			goto out_unlock;
> > +		}
> > +	} else {
> > +		closid_free(io_alloc_closid);
> > +	}
> > +
> > +	ret = resctrl_arch_io_alloc_enable(r, enable);
> I missed this earlier ... if enable == true then a CLOSID would have been allocated
> at this point but resctrl_arch_io_alloc_enable() is not expected to change the arch's
> state when it fails. io_alloc arch state would thus remain "disabled" while the io_alloc
> CLOSID is allocated. io_alloc CLOSID should free'd on failure of
> resctrl_arch_io_alloc_enable() to address this scenario.

Sure. Will add the check:

ret = resctrl_arch_io_alloc_enable(r, enable);

if (enable && ret) {
          rdt_last_cmd_puts("Failed to enable io_alloc feature\n");
           closid_free(io_alloc_closid);
}


> > +
> > +out_unlock:
> > +	mutex_unlock(&rdtgroup_mutex);
> > +	cpus_read_unlock();
> > +
> > +	return ret ?: nbytes;
> > +}
> > diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
> > index a18ed8889396..26ab8f9b30d8 100644
> > --- a/fs/resctrl/internal.h
> > +++ b/fs/resctrl/internal.h
> > @@ -390,6 +390,8 @@ void rdt_staged_configs_clear(void);
> >   
> >   bool closid_allocated(unsigned int closid);
> >   
> > +bool closid_alloc_fixed(u32 closid);
> > +
> >   int resctrl_find_cleanest_closid(void);
> >   
> >   void *rdt_kn_parent_priv(struct kernfs_node *kn);
> > @@ -428,6 +430,15 @@ ssize_t mbm_L3_assignments_write(struct kernfs_open_file *of, char *buf, size_t
> >   				 loff_t off);
> >   int resctrl_io_alloc_show(struct kernfs_open_file *of, struct seq_file *seq, void *v);
> >   
> > +int rdtgroup_init_cat(struct resctrl_schema *s, u32 closid);
> > +
> > +enum resctrl_conf_type resctrl_peer_type(enum resctrl_conf_type my_type);
> > +
> > +ssize_t resctrl_io_alloc_write(struct kernfs_open_file *of, char *buf,
> > +			       size_t nbytes, loff_t off);
> > +
> > +const char *rdtgroup_name_by_closid(int closid);
> Could this please keep the closid type consistent as u32?


Sure. Will do.

Thanks

Babu