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Date: Fri, 8 Dec 2023 13:57:33 -0800
From: Tony Luck <tony.luck@...el.com>
To: Peter Newman <peternewman@...gle.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>,
Reinette Chatre <reinette.chatre@...el.com>,
Jonathan Corbet <corbet@....net>,
Shuah Khan <skhan@...uxfoundation.org>, x86@...nel.org,
Shaopeng Tan <tan.shaopeng@...itsu.com>,
James Morse <james.morse@....com>,
Jamie Iles <quic_jiles@...cinc.com>,
Babu Moger <babu.moger@....com>,
Randy Dunlap <rdunlap@...radead.org>,
linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
patches@...ts.linux.dev
Subject: Re: [PATCH v6 1/3] x86/resctrl: Add mount option "mba_MBps_event"
On Fri, Dec 08, 2023 at 10:17:08AM -0800, Peter Newman wrote:
> Hi Tony,
>
> On Thu, Dec 7, 2023 at 11:56 AM Tony Luck <tony.luck@...el.com> wrote:
> >
> > The MBA Software Controller(mba_sc) is a feedback loop that uses
> > measurements of local memory bandwidth to adjust MBA throttling levels
> > to keep workloads in a resctrl group within a target bandwidth set in
> > the schemata file.
> >
> > Users may want to use total memory bandwidth instead of local to handle
> > workloads that have poor NUMA localization.
> >
> > Add a new mount option "mba_MBps_event={event_name}" where event_name
> > is one of "mbm_Local_bytes" or "mbm_total_bytes" that allows a user to
>
> It's "mbm_local_bytes" in the matching logic later on.
Clearly my left hand operating the shift key is not well synchronized
with my right hand moving from "_" to "l".
Will fix.
> > diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> > index a4f1aa15f0a2..8b9b8f664324 100644
> > --- a/arch/x86/kernel/cpu/resctrl/internal.h
> > +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> > @@ -58,7 +58,8 @@ struct rdt_fs_context {
> > struct kernfs_fs_context kfc;
> > bool enable_cdpl2;
> > bool enable_cdpl3;
> > - bool enable_mba_mbps;
> > + bool enable_mba_mbps_local;
> > + bool enable_mba_mbps_total;
> > bool enable_debug;
> > };
> >
> > diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> > index f136ac046851..d9e590f1cbc3 100644
> > --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> > +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> > @@ -431,9 +431,10 @@ static int __mon_event_count(u32 rmid, struct rmid_read *rr)
> > */
> > static void mbm_bw_count(u32 rmid, struct rmid_read *rr)
> > {
> > - struct mbm_state *m = &rr->d->mbm_local[rmid];
> > u64 cur_bw, bytes, cur_bytes;
> > + struct mbm_state *m;
> >
> > + m = get_mbm_state(rr->d, rmid, rr->evtid);
>
> WARN_ON(m == NULL) since we assume the caller has confirmed rr->evtid
> is an MBM event?
Will add this WARN_ON (though I'll write "WARN_ON(!m);" rather than "== NULL").
>
> > cur_bytes = rr->val;
> > bytes = cur_bytes - m->prev_bw_bytes;
> > m->prev_bw_bytes = cur_bytes;
> > @@ -521,19 +522,21 @@ static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_domain *dom_mbm)
> > u32 closid, rmid, cur_msr_val, new_msr_val;
> > struct mbm_state *pmbm_data, *cmbm_data;
> > u32 cur_bw, delta_bw, user_bw;
> > + enum resctrl_event_id evt_id;
> > struct rdt_resource *r_mba;
> > struct rdt_domain *dom_mba;
> > struct list_head *head;
> > struct rdtgroup *entry;
> >
> > - if (!is_mbm_local_enabled())
> > + if (!is_mbm_enabled())
> > return;
> >
> > r_mba = &rdt_resources_all[RDT_RESOURCE_MBA].r_resctrl;
> > + evt_id = r_mba->membw.mba_mbps_event;
> >
> > closid = rgrp->closid;
> > rmid = rgrp->mon.rmid;
> > - pmbm_data = &dom_mbm->mbm_local[rmid];
> > + pmbm_data = get_mbm_state(dom_mbm, rmid, evt_id);
>
> One defensive WARN_ON((!pmbm_data) for this function to ensure evt_id
> is valid for this call and the ones in the loop below?
Will add this. And the WARN_ON(!cmbm_data); in the loop.
> > @@ -2466,8 +2468,12 @@ static int rdt_enable_ctx(struct rdt_fs_context *ctx)
> > goto out_cdpl2;
> > }
> >
> > - if (ctx->enable_mba_mbps) {
> > - ret = set_mba_sc(true);
> > + if (ctx->enable_mba_mbps_local || ctx->enable_mba_mbps_total) {
> > + if (ctx->enable_mba_mbps_total)
> > + mba_mbps_event = QOS_L3_MBM_TOTAL_EVENT_ID;
> > + else
> > + mba_mbps_event = QOS_L3_MBM_LOCAL_EVENT_ID;
>
> Total takes precedence over local when the user picks both.
Harmless ... but see below.
> > + ret = set_mba_sc(true, mba_mbps_event);
> > if (ret)
> > goto out_cdpl3;
> > }
> > @@ -2683,15 +2689,17 @@ enum rdt_param {
> > Opt_cdp,
> > Opt_cdpl2,
> > Opt_mba_mbps,
> > + Opt_mba_mbps_event,
> > Opt_debug,
> > nr__rdt_params
> > };
> >
> > static const struct fs_parameter_spec rdt_fs_parameters[] = {
> > - fsparam_flag("cdp", Opt_cdp),
> > - fsparam_flag("cdpl2", Opt_cdpl2),
> > - fsparam_flag("mba_MBps", Opt_mba_mbps),
> > - fsparam_flag("debug", Opt_debug),
> > + fsparam_flag("cdp", Opt_cdp),
> > + fsparam_flag("cdpl2", Opt_cdpl2),
> > + fsparam_flag("mba_MBps", Opt_mba_mbps),
> > + fsparam_string("mba_MBps_event", Opt_mba_mbps_event),
> > + fsparam_flag("debug", Opt_debug),
> > {}
> > };
> >
> > @@ -2715,7 +2723,25 @@ static int rdt_parse_param(struct fs_context *fc, struct fs_parameter *param)
> > case Opt_mba_mbps:
> > if (!supports_mba_mbps())
> > return -EINVAL;
> > - ctx->enable_mba_mbps = true;
> > + if (is_mbm_local_enabled())
> > + ctx->enable_mba_mbps_local = true;
> > + else
> > + return -EINVAL;
> > + return 0;
> > + case Opt_mba_mbps_event:
> > + if (!supports_mba_mbps())
> > + return -EINVAL;
> > + if (!strcmp("mbm_local_bytes", param->string)) {
> > + if (!is_mbm_local_enabled())
> > + return -EINVAL;
> > + ctx->enable_mba_mbps_local = true;
> > + } else if (!strcmp("mbm_total_bytes", param->string)) {
> > + if (!is_mbm_total_enabled())
> > + return -EINVAL;
> > + ctx->enable_mba_mbps_total = true;
> > + } else {
> > + return -EINVAL;
>
> It looks like if I pass
> "mba_MBps_event=mbm_total_bytes,mba_MBps_event=mbm_local_bytes" I can
> set both flags true.
That's going to be confusing. I'll add code to stop the user from
passing both options.
> > --
> > 2.41.0
> >
>
> Consider the setting-both-events quirk and a little bit of defensive
> programming for get_mbm_data() returning NULL.
>
> Assuming the case of "Local" is fixed in the commit message:
>
> Reviewed-by: Peter Newman <peternewman@...gle.com>
Thanks for reviewing, and for the tags for parts 2 & 3.
-Tony
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