linux-kernel - Re: [PATCH v8 17/25] x86/resctrl: Add the interface to assign/update counter assignment

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Message-ID: <c36e0c76-1666-4a31-984e-1ee6aed2e414@intel.com>
Date: Fri, 18 Oct 2024 08:59:31 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: <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>,
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	<jpoimboe@...nel.org>, <rick.p.edgecombe@...el.com>,
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	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<eranian@...gle.com>, <james.morse@....com>
Subject: Re: [PATCH v8 17/25] x86/resctrl: Add the interface to assign/update
 counter assignment

Hi Babu,

On 10/17/24 3:56 PM, Moger, Babu wrote:
> On 10/15/2024 10:25 PM, Reinette Chatre wrote:
>> On 10/9/24 10:39 AM, Babu Moger wrote:

>>> + */
>>> +int rdtgroup_assign_cntr_event(struct rdt_resource *r, struct rdtgroup *rdtgrp,
>>> +                   struct rdt_mon_domain *d, enum resctrl_event_id evtid)
>>> +{
>>> +    int index = MBM_EVENT_ARRAY_INDEX(evtid);
>>> +    int cntr_id = rdtgrp->mon.cntr_id[index];
>>> +    int ret;
>>> +
>>> +    /*
>>> +     * Allocate a new counter id to the event if the counter is not
>>> +     * assigned already.
>>> +     */
>>> +    if (cntr_id == MON_CNTR_UNSET) {
>>> +        cntr_id = mbm_cntr_alloc(r);
>>> +        if (cntr_id < 0) {
>>> +            rdt_last_cmd_puts("Out of MBM assignable counters\n");
>>> +            return -ENOSPC;
>>> +        }
>>> +        rdtgrp->mon.cntr_id[index] = cntr_id;
>>> +    }
>>> +
>>> +    if (!d) {
>>> +        list_for_each_entry(d, &r->mon_domains, hdr.list) {
>>> +            ret = resctrl_arch_config_cntr(r, d, evtid, rdtgrp->mon.rmid,
>>> +                               rdtgrp->closid, cntr_id, true);
>>> +            if (ret)
>>> +                goto out_done_assign;
>>> +
>>> +            set_bit(cntr_id, d->mbm_cntr_map);
>>
>> The code pattern above is repeated four times in this work, twice in
>> rdtgroup_assign_cntr_event() and twice in rdtgroup_unassign_cntr_event(). This
>> duplication should be avoided. It can be done in a function that also resets
>> the architectural state.
> 
> Are you suggesting to combine rdtgroup_assign_cntr_event() and rdtgroup_unassign_cntr_event()?

No. My comment was about the following pattern that is repeated four times:
	...
	ret = resctrl_arch_config_cntr(...)
	if (ret)
		...
	set_bit()/clear_bit()
	...

> It can be done. We need a flag to tell if it is a assign or unassign.

There is already a flag that is used by resctrl_arch_config_cntr(), the same parameters
as resctrl_arch_config_cntr() can be used for a wrapper that just calls
resctrl_arch_config_cntr() directly and uses that same flag to
select between set_bit() and clear_bit(). This wrapper can then also include
the reset of architectural state.

Also, I do not think we need atomic bitops here so these can be __set_bit()
and __clear_bit() that also matches how bits of mbm_cntr_free_map are managed
earlier in series.

Reinette