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Message-ID: <b2e16be8-c203-4acc-89aa-5af29b7d6e63@amd.com>
Date: Fri, 20 Jun 2025 16:58:29 -0500
From: "Moger, Babu" <bmoger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
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 Reinette,
On 6/17/2025 11:03 PM, Reinette Chatre wrote:
> 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"
Sure.
>
>> from I/O devices into the L3 cache. By directly caching data from I/O
>
> Drop L3
>
Sure.
>> 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?
Will remove it.
>
>> 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.
>
Sure. Yea. Already added in show().
>> +
>>
>> 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.
Sure.
>
>> + 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"
Sure.
>
>> + }
>> +
>> + 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.
Yes. Check not required.
>
>> + 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.
Yes. Added it.
>
>> + 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
>
Thanks
Babu
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