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Date: Fri, 28 Oct 2022 15:16:33 +0000
From: "Moger, Babu" <Babu.Moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
"corbet@....net" <corbet@....net>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"mingo@...hat.com" <mingo@...hat.com>,
"bp@...en8.de" <bp@...en8.de>
CC: "fenghua.yu@...el.com" <fenghua.yu@...el.com>,
"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
"x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
"paulmck@...nel.org" <paulmck@...nel.org>,
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<pawan.kumar.gupta@...ux.intel.com>,
"jmattson@...gle.com" <jmattson@...gle.com>,
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"Das1, Sandipan" <Sandipan.Das@....com>,
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Subject: RE: [PATCH v7 05/12] x86/resctrl: Detect and configure Slow Memory
Bandwidth allocation
[AMD Official Use Only - General]
Hi Reinette,
> -----Original Message-----
> From: Reinette Chatre <reinette.chatre@...el.com>
> Sent: Thursday, October 27, 2022 1:38 PM
> To: Moger, Babu <Babu.Moger@....com>; corbet@....net;
> tglx@...utronix.de; mingo@...hat.com; bp@...en8.de
> Cc: fenghua.yu@...el.com; dave.hansen@...ux.intel.com; x86@...nel.org;
> hpa@...or.com; paulmck@...nel.org; akpm@...ux-foundation.org;
> quic_neeraju@...cinc.com; rdunlap@...radead.org;
> damien.lemoal@...nsource.wdc.com; songmuchun@...edance.com;
> peterz@...radead.org; jpoimboe@...nel.org; pbonzini@...hat.com;
> chang.seok.bae@...el.com; pawan.kumar.gupta@...ux.intel.com;
> jmattson@...gle.com; daniel.sneddon@...ux.intel.com; Das1, Sandipan
> <Sandipan.Das@....com>; tony.luck@...el.com; james.morse@....com;
> linux-doc@...r.kernel.org; linux-kernel@...r.kernel.org;
> bagasdotme@...il.com; eranian@...gle.com
> Subject: Re: [PATCH v7 05/12] x86/resctrl: Detect and configure Slow Memory
> Bandwidth allocation
>
> Hi Babu,
>
> On 10/27/2022 8:30 AM, Moger, Babu wrote:
> > On 10/26/22 15:23, Reinette Chatre wrote:
> >> On 10/26/2022 12:07 PM, Moger, Babu wrote:
> >>> On 10/25/22 18:43, Reinette Chatre wrote:
> >>>> On 10/17/2022 3:26 PM, Babu Moger wrote:
> >>>>
> >>>> ...
> >>>>
> >>>>> @@ -2845,7 +2846,8 @@ static int rdtgroup_init_alloc(struct
> >>>>> rdtgroup *rdtgrp)
> >>>>>
> >>>>> list_for_each_entry(s, &resctrl_schema_all, list) {
> >>>>> r = s->res;
> >>>>> - if (r->rid == RDT_RESOURCE_MBA) {
> >>>>> + if (r->rid == RDT_RESOURCE_MBA ||
> >>>>> + r->rid == RDT_RESOURCE_SMBA) {
> >>>>> rdtgroup_init_mba(r, rdtgrp->closid);
> >>>>> if (is_mba_sc(r))
> >>>>> continue;
> >>>> The above hunk and the ones that follow are unexpected.
> >>> I am thinking the above check is required, It is updating the
> >>> staged_config with default values. Right now, the default value for
> >>> SMBA is same as MBA default value. So, I used this code to initialize.
> >>>
> >>> Did I miss something?
> >> As I described in the following comments my concern is related to all
> >> the software controller code still executing for SMBA. Yes, in the
> >> above hunk SMBA would need (some of) rdtgroup_init_mba() ... but note
> >> that it contains software controller checks and in the above hunk its
> >> call is also followed by another software controller check.
> >>
> >> The software controller is just applicable to MBA and these checks
> >> have been isolated to the MBA resource. Using it for SMBA that does
> >> not support software controller at all is making the code harder to
> >> follow and sets this code up for future mistakes. I think it would
> >> make the code easier to understand if this is made very clear that
> >> software controller is not applicable to SMBA at all instead of repurposing
> these flows.
> >
> > Yes. Understood. How about this? I feel this is much more cleaner.
> >
> > diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > index e5a48f05e787..d91a6a513681 100644
> > --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > @@ -2845,16 +2845,18 @@ static int rdtgroup_init_alloc(struct rdtgroup
> > *rdtgrp)
> >
> > list_for_each_entry(s, &resctrl_schema_all, list) {
> > r = s->res;
> > - if (r->rid == RDT_RESOURCE_MBA) {
> > + if (r->rid == RDT_RESOURCE_MBA ||
> > + r->rid == RDT_RESOURCE_SMBA) {
> > rdtgroup_init_mba(r, rdtgrp->closid);
> > - if (is_mba_sc(r))
> > - continue;
> > } else {
> > ret = rdtgroup_init_cat(s, rdtgrp->closid);
> > if (ret < 0)
> > return ret;
> > }
> >
> > + if (is_mba_sc(r))
> > + continue;
> > +
> > ret = resctrl_arch_update_domains(r, rdtgrp->closid);
> > if (ret < 0) {
> > rdt_last_cmd_puts("Failed to initialize
> > allocations\n");
> >
>
> I do not see how that move changes what is run in the SMBA case and it ignores
> the
> is_mba_sc() call within rdtgroup_init_mba(). How about making is_mba_sc()
> more robust in support of your original snippet?
>
> Something like:
>
> bool is_mba_sc(struct rdt_resource *r)
> {
> if (!r)
> return
> rdt_resources_all[RDT_RESOURCE_MBA].r_resctrl.membw.mba_sc;
>
> if (r->rid != RDT_RESOURCE_MBA)
> return false;
>
> return r->membw.mba_sc;
> }
Yes. Sure. That should work.
Thanks
Babu
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