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Message-ID: <773d02ba-64d0-4c03-968e-f303ffefc4dd@amd.com>
Date: Thu, 26 Sep 2024 14:39:45 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.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 v7 20/24] x86/resctrl: Introduce the interface to switch
between monitor modes
Hi Reinette,
On 9/19/24 12:38, Reinette Chatre wrote:
> Hi Babu,
>
> On 9/4/24 3:21 PM, 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>
>> ---
>> v7: Changed the interface name to mbm_assign_mode.
>> Removed the references of ABMC.
>> Added the changes to reset global and domain bitmaps.
>> Added the changes to reset rmid.
>>
>> v6: Changed the mode name to mbm_cntr_assign.
>> Moved all the FS related code here.
>> Added changes to reset mbm_cntr_map and resctrl group counters.
>> ""
>> v5: Change log and mode description text correction.
>>
>> v4: Minor commit text changes. Keep the default to ABMC when supported.
>> Fixed comments to reflect changed interface "mbm_mode".
>>
>> v3: New patch to address the review comments from upstream.
>> ---
>> Documentation/arch/x86/resctrl.rst | 15 ++++++
>> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 74 +++++++++++++++++++++++++-
>> 2 files changed, 88 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
>> index ff5397d19704..743c0b64a330 100644
>> --- a/Documentation/arch/x86/resctrl.rst
>> +++ b/Documentation/arch/x86/resctrl.rst
>> @@ -290,6 +290,21 @@ with the following files:
>> than 'num_mbm_cntrs' to be created. Reading the mbm files may report 'Unavailable'
>> if there is no hardware resource assigned.
>>
>> + * To enable ABMC feature:
>
> The separation between fs and arch did not make it to this patch?
My bad. Will change the text.
>
>> + ::
>> +
>> + # echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> +
>> + * To enable the legacy monitoring feature:
>
> "legacy" -> "default"?
Sure.
>
>> + ::
>> +
>> + # echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> +
>> + The MBM event counters will reset when mbm_assign_mode is changed. Moving to
>
> "will reset" -> "may reset"? Please also be clear on what is meant with "MBM event counter".
It "will reset".
> Note that "counter" has a very specific meaning in this work and after considering that
> it is not clear if "MBM event counter will reset" means that the counters are no longer
> assigned or if it means that the counts associated with events will be reset.
How about
"The MBM event counters(mbm_total_bytes and mbm_local_bytes) associated
with the event will reset when mbm_assign_mode is changed."
>
>> + mbm_cntr_assign will require users to assign the counters to the events to
>> + read the events. Otherwise, the MBM event counters will return "Unassigned"
>> + when read.
>> +
>> "num_mbm_cntrs":
>> The number of monitoring counters available for assignment.
>>
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index bf94e4e05540..7a8ece12d7da 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -895,6 +895,77 @@ static int rdtgroup_mbm_assign_mode_show(struct kernfs_open_file *of,
>> return 0;
>> }
>>
>> +static void rdtgroup_mbm_cntr_reset(struct rdt_resource *r)
>
> It is not clear why this has "rdtgroup" prefix since it is not specific to
> a resource group but a global action that resets all counters.
Sure. Will remote prefix.
>
>> +{
>> + 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;
>> + }
>> + }
>> +}
>> +
>> +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;
>> + }
>> +
>> + if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
>> + rdtgroup_mbm_cntr_reset(r);
>
> Should this reset not happen only after the hardware state was changed
> successfully? If the arch change failed then this may lead to inconsistent
> state.
Sure. Will move after the mode is changed.
>
>> + ret = resctrl_arch_mbm_cntr_assign_set(r, enable);
>> + }
>> +
>> +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)
>> {
>> @@ -2107,9 +2178,10 @@ 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
>
--
Thanks
Babu Moger
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