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Message-ID: <4d49182f-6185-49df-b9bf-29fbd17dccf6@intel.com>
Date: Tue, 15 Oct 2024 20:36:55 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: 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 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
> +
> + * To enable default monitoring mode:
> + ::
> +
> + # echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
extra spaces
> +
> + 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/
> + 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
> + }
> +}
> +
> +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.
> + 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
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