linux-kernel - RE: [PATCH v4 1/2] x86/resctrl: Pass domain to target CPU

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Message-ID: <SJ1PR11MB6083C8DF1FD451CD43D6726FFC222@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Tue, 5 Mar 2024 16:37:25 +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: 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>, Drew Fustini
	<dfustini@...libre.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 v4 1/2] x86/resctrl: Pass domain to target CPU

> If I understand correctly that would always look for a valid "cpu"
> even when none is needed. Not quite what I proposed but should
> work. Just some wasted cycles in a non critical path. 

Reinette,

Sorry for misunderstanding. You are right. Assignment to msr_param.dom
can also be deferred to the same point. Like this:

        list_for_each_entry(d, &r->domains, list) {
                hw_dom = resctrl_to_arch_dom(d);
                msr_param.res = NULL;
                for (t = 0; t < CDP_NUM_TYPES; t++) {
                        cfg = &hw_dom->d_resctrl.staged_config[t];
                        if (!cfg->have_new_ctrl)
                                continue;

                        idx = get_config_index(closid, t);
                        if (cfg->new_ctrl == hw_dom->ctrl_val[idx])
                                continue;
                        hw_dom->ctrl_val[idx] = cfg->new_ctrl;

                        if (!msr_param.res) {
                                msr_param.low = idx;
                                msr_param.high = msr_param.low + 1;
                                msr_param.res = r;
                                msr_param.dom = d;
                                cpu = cpumask_any(&d->cpu_mask);
                        } else {
                                msr_param.low = min(msr_param.low, idx);
                                msr_param.high = max(msr_param.high, idx + 1);
                        }
                }
                if (msr_param.res)
                        smp_call_function_single(cpu, rdt_ctrl_update, &msr_param, 1);
        }

-Tony