linux-kernel - RE: [PATCH v8 5/7] x86/resctrl: Add "mba_MBps_event" file to ctrl

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Message-ID: <SJ1PR11MB6083839383802DC9127C5CD2FC592@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Tue, 12 Nov 2024 23:42:44 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: "Chatre, Reinette" <reinette.chatre@...el.com>, "Yu, Fenghua"
	<fenghua.yu@...el.com>, Peter Newman <peternewman@...gle.com>, "Jonathan
 Corbet" <corbet@....net>, Shuah Khan <skhan@...uxfoundation.org>,
	"x86@...nel.org" <x86@...nel.org>
CC: James Morse <james.morse@....com>, Jamie Iles <quic_jiles@...cinc.com>,
	Babu Moger <babu.moger@....com>, Randy Dunlap <rdunlap@...radead.org>,
	"Shaopeng Tan (Fujitsu)" <tan.shaopeng@...itsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"patches@...ts.linux.dev" <patches@...ts.linux.dev>
Subject: RE: [PATCH v8 5/7] x86/resctrl: Add "mba_MBps_event" file to ctrl_mon
 directories

> > +static int set_mba_sc(bool mba_sc)
> > +{
> > +   struct rftype *rft;
> > +
> > +   rft = rdtgroup_get_rftype_by_name("mba_MBps_event");
> > +   if (rft)
> > +           rft->fflags = enable ? RFTYPE_CTRL_BASE : 0;
>
> I think this sets this file to be created for all CTRL groups, even when not supporting
> monitoring?

No. The calling sequence is:

rdt_get_tree()
    rdt_enable_ctx()

        if (ctx->enable_mba_mbps) {
                ret = set_mba_sc(true);
                if (ret)
                        goto out_cdpl3;
        }

So set_mba_sc() is only called when the mba_MBps mount option has been used. So
mba_mbps_event_init() isn't called.

Note that on unmount of the resctrl file system rdt_kill_sb() calls rdt_disable_ctx()
which calls set_mba_sc(false) which will clear rft->fflags on systems which support
mba_MBps.

-Tony