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Message-ID: <d6d469e0-b5ee-4e19-917e-a3bb4075fd27@intel.com>
Date: Tue, 17 Jun 2025 21:03:46 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Babu Moger <babu.moger@....com>, <corbet@....net>, <tony.luck@...el.com>,
<Dave.Martin@....com>, <james.morse@....com>, <tglx@...utronix.de>,
<mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>
CC: <x86@...nel.org>, <hpa@...or.com>, <akpm@...ux-foundation.org>,
<paulmck@...nel.org>, <rostedt@...dmis.org>, <thuth@...hat.com>,
<ardb@...nel.org>, <gregkh@...uxfoundation.org>, <seanjc@...gle.com>,
<thomas.lendacky@....com>, <pawan.kumar.gupta@...ux.intel.com>,
<perry.yuan@....com>, <yosry.ahmed@...ux.dev>, <kai.huang@...el.com>,
<xiaoyao.li@...el.com>, <peterz@...radead.org>, <kan.liang@...ux.intel.com>,
<mario.limonciello@....com>, <xin3.li@...el.com>, <sohil.mehta@...el.com>,
<chang.seok.bae@...el.com>, <andrew.cooper3@...rix.com>,
<ebiggers@...gle.com>, <ak@...ux.intel.com>, <xin@...or.com>,
<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 8/8] fs/resctrl: Introduce interface to modify io_alloc
Capacity Bit Masks
Hi Babu,
On 6/11/25 2:23 PM, Babu Moger wrote:
> "io_alloc" feature is a mechanism that enables direct insertion of data
""io_alloc" feature is a mechanism that enables" -> ""io_alloc" feature enables"
> from I/O devices into the L3 cache. By directly caching data from I/O
Drop L3
> devices rather than first storing the I/O data in DRAM, it reduces the
> demands on DRAM bandwidth and reduces latency to the processor consuming
> the I/O data.
>
> "io_alloc" feature uses the highest CLOSID to route the traffic from I/O
How is the CLOSID related here?
> devices. Provide the interface to modify io_alloc CBMs (Capacity Bit Mask)
> when feature is enabled.
>
> Signed-off-by: Babu Moger <babu.moger@....com>
> ---
...
> ---
> Documentation/filesystems/resctrl.rst | 13 ++++
> fs/resctrl/ctrlmondata.c | 4 +-
> fs/resctrl/internal.h | 2 +
> fs/resctrl/rdtgroup.c | 89 ++++++++++++++++++++++++++-
> 4 files changed, 105 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
> index b31748ec8c61..ae1157dcb4a3 100644
> --- a/Documentation/filesystems/resctrl.rst
> +++ b/Documentation/filesystems/resctrl.rst
> @@ -181,6 +181,19 @@ related to allocation:
> # cat /sys/fs/resctrl/info/L3/io_alloc_cbm
> 0=ffff;1=ffff
>
> + CBM can be configured by writing to the interface.
> +
> + Example::
> +
> + # echo 1=FF > /sys/fs/resctrl/info/L3/io_alloc_cbm
> + # cat /sys/fs/resctrl/info/L3/io_alloc_cbm
> + 0=ffff;1=00ff
> +
> + When CDP is enabled, io_alloc directs traffic using the highest CLOSID
> + linked to an L3CODE resource. Although CBMs can be accessed through
> + either L3CODE or L3DATA resources, any updates to the schemata are
> + always routed through L3CODE.
Please do not commit resctrl to this implementation by documenting it as part of
user interface. Could snippet about CDP I shared in patch 6 be placed here as
a replacement? Not the usage of *may* to keep implementation options open.
> +
>
> Memory bandwidth(MB) subdirectory contains the following files
> with respect to allocation:
> diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
> index 6409637b4de6..f3e5e697945c 100644
> --- a/fs/resctrl/ctrlmondata.c
> +++ b/fs/resctrl/ctrlmondata.c
> @@ -148,8 +148,8 @@ static bool cbm_validate(char *buf, u32 *data, struct rdt_resource *r)
> * Read one cache bit mask (hex). Check that it is valid for the current
> * resource type.
> */
> -static int parse_cbm(struct rdt_parse_data *data, struct resctrl_schema *s,
> - struct rdt_ctrl_domain *d)
> +int parse_cbm(struct rdt_parse_data *data, struct resctrl_schema *s,
> + struct rdt_ctrl_domain *d)
> {
> enum rdtgrp_mode mode = data->mode;
> struct resctrl_staged_config *cfg;
> diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
> index 10a3188ffa54..755f23934295 100644
> --- a/fs/resctrl/internal.h
> +++ b/fs/resctrl/internal.h
> @@ -382,6 +382,8 @@ bool closid_allocated(unsigned int closid);
> int resctrl_find_cleanest_closid(void);
> void show_doms(struct seq_file *s, struct resctrl_schema *schema,
> char *name, int closid);
> +int parse_cbm(struct rdt_parse_data *data, struct resctrl_schema *s,
> + struct rdt_ctrl_domain *d);
>
> #ifdef CONFIG_RESCTRL_FS_PSEUDO_LOCK
> int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp);
> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
> index 0c2d2cf4baa1..f6c44fae4b72 100644
> --- a/fs/resctrl/rdtgroup.c
> +++ b/fs/resctrl/rdtgroup.c
> @@ -2037,6 +2037,92 @@ static int resctrl_io_alloc_cbm_show(struct kernfs_open_file *of,
> return ret;
> }
>
> +static int resctrl_io_alloc_parse_line(char *line, struct rdt_resource *r,
> + struct resctrl_schema *s, u32 closid)
> +{
> + struct rdt_parse_data data;
> + struct rdt_ctrl_domain *d;
> + char *dom = NULL, *id;
> + unsigned long dom_id;
> +
> +next:
> + if (!line || line[0] == '\0')
> + return 0;
> +
> + dom = strsep(&line, ";");
> + id = strsep(&dom, "=");
> + if (!dom || kstrtoul(id, 10, &dom_id)) {
> + rdt_last_cmd_puts("Missing '=' or non-numeric domain\n");
> + return -EINVAL;
> + }
> +
> + dom = strim(dom);
> + list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
> + if (d->hdr.id == dom_id) {
> + data.buf = dom;
> + data.mode = RDT_MODE_SHAREABLE;
> + data.closid = closid;
> + if (parse_cbm(&data, s, d))
> + return -EINVAL;
> + goto next;
> + }
> + }
> + return -EINVAL;
> +}
> +
> +static ssize_t resctrl_io_alloc_cbm_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;
> + u32 io_alloc_closid;
> + int ret = 0;
> +
> + /* Valid input requires a trailing newline */
> + if (nbytes == 0 || buf[nbytes - 1] != '\n')
> + return -EINVAL;
> +
> + buf[nbytes - 1] = '\0';
> +
> + if (!r->cache.io_alloc_capable) {
> + rdt_last_cmd_puts("io_alloc feature is not supported on the resource\n");
rdt_last_cmd_puts() requires rdtgroup_mutex to be held.
> + return -EINVAL;
> + }
> +
> + cpus_read_lock();
> + mutex_lock(&rdtgroup_mutex);
> +
> + rdt_last_cmd_clear();
> + rdt_staged_configs_clear();
> +
> + if (!resctrl_arch_get_io_alloc_enabled(r)) {
> + rdt_last_cmd_puts("io_alloc feature is not enabled\n");
> + ret = -EINVAL;
> + goto cbm_write_out;
can just be "out"
> + }
> +
> + io_alloc_closid = resctrl_io_alloc_closid_get(r);
> + if (io_alloc_closid < 0) {
Similar to other places, since this is preceded by resctrl_arch_get_io_alloc_enabled(r)
passing the io_alloc_closid has to be valid and can use proposed resctrl_io_alloc_closid()
helper to simplify the code.
> + rdt_last_cmd_puts("Max CLOSID to support io_alloc is not available\n");
> + ret = -EINVAL;
> + goto cbm_write_out;
> + }
> +
> + ret = resctrl_io_alloc_parse_line(buf, r, resctrl_schema_io_alloc(s),
> + io_alloc_closid);
Here too I think both schemata needs to be updated.
> + if (ret)
> + goto cbm_write_out;
> +
> + ret = resctrl_arch_update_domains(r, io_alloc_closid);
> +
> +cbm_write_out:
> + rdt_staged_configs_clear();
> + mutex_unlock(&rdtgroup_mutex);
> + cpus_read_unlock();
> +
> + return ret ?: nbytes;
> +}
> +
> /* rdtgroup information files for one cache resource. */
> static struct rftype res_common_files[] = {
> {
> @@ -2198,9 +2284,10 @@ static struct rftype res_common_files[] = {
> },
> {
> .name = "io_alloc_cbm",
> - .mode = 0444,
> + .mode = 0644,
> .kf_ops = &rdtgroup_kf_single_ops,
> .seq_show = resctrl_io_alloc_cbm_show,
> + .write = resctrl_io_alloc_cbm_write,
> },
> {
> .name = "mba_MBps_event",
Reinette
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