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Message-ID: <51b47b50-1b83-6565-e7da-14d4de0b15c8@amd.com>
Date: Fri, 18 Oct 2024 10:13:50 -0500
From: "Moger, Babu" <bmoger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
Babu Moger <babu.moger@....com>, corbet@....net, fenghua.yu@...el.com,
tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
dave.hansen@...ux.intel.com
Cc: x86@...nel.org, hpa@...or.com, paulmck@...nel.org, rdunlap@...radead.org,
tj@...nel.org, peterz@...radead.org, yanjiewtw@...il.com,
kim.phillips@....com, lukas.bulwahn@...il.com, seanjc@...gle.com,
jmattson@...gle.com, leitao@...ian.org, jpoimboe@...nel.org,
rick.p.edgecombe@...el.com, kirill.shutemov@...ux.intel.com,
jithu.joseph@...el.com, kai.huang@...el.com, kan.liang@...ux.intel.com,
daniel.sneddon@...ux.intel.com, pbonzini@...hat.com, sandipan.das@....com,
ilpo.jarvinen@...ux.intel.com, peternewman@...gle.com,
maciej.wieczor-retman@...el.com, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, eranian@...gle.com, james.morse@....com
Subject: Re: [PATCH v8 21/25] x86/resctrl: Introduce the interface to switch
between monitor modes
Hi Reinette,
On 10/15/2024 10:36 PM, Reinette Chatre wrote:
> Hi Babu,
>
> On 10/9/24 10:39 AM, Babu Moger wrote:
>> Introduce interface to switch between mbm_cntr_assign and default modes.
>>
>> $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> [mbm_cntr_assign]
>> default
>>
>> To enable the "mbm_cntr_assign" mode:
>> $ echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>>
>> To enable the default monitoring mode:
>> $ echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>>
>> MBM event counters will reset when mbm_assign_mode is changed.
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
>
> ...
>
>> ---
>> Documentation/arch/x86/resctrl.rst | 15 ++++++
>> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 75 +++++++++++++++++++++++++-
>> 2 files changed, 89 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
>> index 99ee9c87952b..d9574078f735 100644
>> --- a/Documentation/arch/x86/resctrl.rst
>> +++ b/Documentation/arch/x86/resctrl.rst
>> @@ -291,6 +291,21 @@ with the following files:
>> that case reading the mbm_total_bytes and mbm_local_bytes may report
>> 'Unavailable' if there is no counter associated with that group.
>>
>> + * To enable "mbm_cntr_assign" mode:
>> + ::
>> +
>> + # echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>
> extra spaces
Sure.
>
>> +
>> + * To enable default monitoring mode:
>> + ::
>> +
>> + # echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>
> extra spaces
Sure
>> +
>> + The MBM events (mbm_total_bytes and/or mbm_local_bytes) associated counters
>
> I did ask you not to copy the text verbatim
> https://lore.kernel.org/all/b38c93bf-4650-45d1-9aca-8b4c4d425886@intel.com/
Outch Yea.
The MBM events (mbm_total_bytes and/or mbm_local_bytes) associated with
counters may reset when mbm_assign_mode is changed.
>
>> + may reset when the mode is changed. Moving to mbm_cntr_assign mode will
>> + require users to assign the counters to the events. Otherwise, the MBM
>
> "will require" -> "require"
>
>> + event counters will return "Unassigned" when read.
>> +
>> "num_mbm_cntrs":
>> The number of monitoring counters available for assignment when the
>> architecture supports mbm_cntr_assign mode.
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index cb2c60c0319e..88eda3cf5c82 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -888,6 +888,78 @@ static int rdtgroup_mbm_assign_mode_show(struct kernfs_open_file *of,
>> return 0;
>> }
>>
>> +static void mbm_cntr_reset(struct rdt_resource *r)
>> +{
>> + struct rdtgroup *prgrp, *crgrp;
>> + struct rdt_mon_domain *dom;
>> +
>> + /*
>> + * Hardware counters will reset after switching the monitor mode.
>> + * Reset the architectural state so that reading of hardware
>> + * counter is not considered as an overflow in the next update.
>> + * Also reset the domain counter bitmap.
>> + */
>> + list_for_each_entry(dom, &r->mon_domains, hdr.list) {
>> + bitmap_zero(dom->mbm_cntr_map, r->mon.num_mbm_cntrs);
>> + resctrl_arch_reset_rmid_all(r, dom);
>> + }
>> +
>> + /* Reset global MBM counter map */
>> + bitmap_fill(r->mon.mbm_cntr_free_map, r->mon.num_mbm_cntrs);
>> +
>> + /* Reset the cntr_id's for all the monitor groups */
>> + list_for_each_entry(prgrp, &rdt_all_groups, rdtgroup_list) {
>> + prgrp->mon.cntr_id[0] = MON_CNTR_UNSET;
>> + prgrp->mon.cntr_id[1] = MON_CNTR_UNSET;
>> + list_for_each_entry(crgrp, &prgrp->mon.crdtgrp_list,
>> + mon.crdtgrp_list) {
>> + crgrp->mon.cntr_id[0] = MON_CNTR_UNSET;
>> + crgrp->mon.cntr_id[1] = MON_CNTR_UNSET;
>> + }
>
> Please use MBM_EVENT_ARRAY_INDEX
Sure.
>
>> + }
>> +}
>> +
>> +static ssize_t rdtgroup_mbm_assign_mode_write(struct kernfs_open_file *of,
>> + char *buf, size_t nbytes, loff_t off)
>> +{
>> + struct rdt_resource *r = of->kn->parent->priv;
>> + int ret = 0;
>> + bool enable;
>> +
>> + /* Valid input requires a trailing newline */
>> + if (nbytes == 0 || buf[nbytes - 1] != '\n')
>> + return -EINVAL;
>> +
>> + buf[nbytes - 1] = '\0';
>> +
>> + cpus_read_lock();
>> + mutex_lock(&rdtgroup_mutex);
>> +
>> + rdt_last_cmd_clear();
>> +
>> + if (!strcmp(buf, "default")) {
>> + enable = 0;
>> + } else if (!strcmp(buf, "mbm_cntr_assign")) {
>> + enable = 1;
>> + } else {
>> + ret = -EINVAL;
>> + rdt_last_cmd_puts("Unsupported assign mode\n");
>> + goto write_exit;
>> + }
>
> Please keep two things in mind:
> * this file is always accessible, whether platform supports assignable
> counters or not.
> * this is resctrl fs code.
>
> So, considering above, how should user interpret the "Unsupported assign mode"?
> Shouldn't it also return this error if a user attempts to enable
> "mbm_cntr_assign" on a platform that does not support this mode?
>
>> +
>> + if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
>
> resctrl_arch_mbm_cntr_assign_enabled() returns true if mbm_cntr_assign
> mode is enabled, but when it returns false it could mean different things:
> platform supports mbm_cntr_assign mode, but it is disabled, or platform
> does not support mbm_cntr_assign mode.
>
> resctrl fs should not rely on all archs to duplicate the all the checking done
> in resctrl_arch_mbm_cntr_assign_set(). It should never ask arch to enable a mode
> that it knows the platform is not capable of.
Agree. This should take care of it. Good catch.
if (!strcmp(buf, "default")) {
enable = 0;
} else if (!strcmp(buf, "mbm_cntr_assign")) {
if (r->mon.mbm_cntr_assignable) {
enable = 1;
} else {
ret = -EINVAL;
rdt_last_cmd_puts("mbm_cntr_assign mode is not supported\n");
goto write_exit;
}
} else {
ret = -EINVAL;
rdt_last_cmd_puts("Unsupported assign mode\n");
goto write_exit;
}
>
>> + ret = resctrl_arch_mbm_cntr_assign_set(r, enable);
>> + if (!ret)
>> + mbm_cntr_reset(r);
>> + }
>> +
>> +write_exit:
>> + mutex_unlock(&rdtgroup_mutex);
>> + cpus_read_unlock();
>> +
>> + return ret ?: nbytes;
>> +}
>> +
>> static int rdtgroup_num_mbm_cntrs_show(struct kernfs_open_file *of,
>> struct seq_file *s, void *v)
>> {
>> @@ -2115,9 +2187,10 @@ static struct rftype res_common_files[] = {
>> },
>> {
>> .name = "mbm_assign_mode",
>> - .mode = 0444,
>> + .mode = 0644,
>> .kf_ops = &rdtgroup_kf_single_ops,
>> .seq_show = rdtgroup_mbm_assign_mode_show,
>> + .write = rdtgroup_mbm_assign_mode_write,
>> .fflags = RFTYPE_MON_INFO,
>> },
>> {
>
> Reinette
>
>
--
- Babu Moger
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