linux-kernel - Re: [PATCH v10 06/10] fs/resctrl: Add user interface to enable/disable io

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Message-ID: <b28ed9df-03cf-412e-b300-2b8499c30fc8@intel.com>
Date: Fri, 24 Oct 2025 16:43:20 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <tony.luck@...el.com>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>
CC: <corbet@....net>, <Dave.Martin@....com>, <james.morse@....com>,
	<x86@...nel.org>, <hpa@...or.com>, <akpm@...ux-foundation.org>,
	<paulmck@...nel.org>, <rdunlap@...radead.org>, <pmladek@...e.com>,
	<kees@...nel.org>, <arnd@...db.de>, <fvdl@...gle.com>, <seanjc@...gle.com>,
	<pawan.kumar.gupta@...ux.intel.com>, <xin@...or.com>,
	<thomas.lendacky@....com>, <sohil.mehta@...el.com>, <jarkko@...nel.org>,
	<chang.seok.bae@...el.com>, <ebiggers@...gle.com>,
	<elena.reshetova@...el.com>, <ak@...ux.intel.com>,
	<mario.limonciello@....com>, <perry.yuan@....com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<peternewman@...gle.com>
Subject: Re: [PATCH v10 06/10] fs/resctrl: Add user interface to
 enable/disable io_alloc feature

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


...

> +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.

> +
> +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?

Reinette