linux-kernel - [PATCH 1/5] x86/intel_rdt: Update control registers only when user really modifies it

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Date:   Fri, 17 Feb 2017 11:38:44 -0800
From:   Vikas Shivappa <vikas.shivappa@...ux.intel.com>
To:     vikas.shivappa@...el.com
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
        tglx@...utronix.de, mingo@...nel.org, peterz@...radead.org,
        ravi.v.shankar@...el.com, tony.luck@...el.com,
        fenghua.yu@...el.com, andi.kleen@...el.com,
        vikas.shivappa@...ux.intel.com
Subject: [PATCH 1/5] x86/intel_rdt: Update control registers only when user really modifies it

When a schemata is updated, the values for all the domains and all
resources are entered.  However, the values for each of them may not
change in many use cases as the user is only updating values for a
subset of resources and domains. The resource control values are updated
via QOS_MSRs which are per package. Change the update to QOS_MSRs to
happen only when the control value on the particular domain is updated.
Hence not sending IPIs on all domains when user updates the control
vals.

Signed-off-by: Vikas Shivappa <vikas.shivappa@...ux.intel.com>
---
 arch/x86/kernel/cpu/intel_rdt_schemata.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt_schemata.c b/arch/x86/kernel/cpu/intel_rdt_schemata.c
index f369cb8..14ba504 100644
--- a/arch/x86/kernel/cpu/intel_rdt_schemata.c
+++ b/arch/x86/kernel/cpu/intel_rdt_schemata.c
@@ -114,9 +114,16 @@ static int update_domains(struct rdt_resource *r, int closid)
 	msr_param.high = msr_param.low + 1;
 	msr_param.res = r;
 
+	/*
+	 * Only update the domains that user has changed.
+	 * There by avoiding unnecessary IPIs.
+	 */
 	list_for_each_entry(d, &r->domains, list) {
-		cpumask_set_cpu(cpumask_any(&d->cpu_mask), cpu_mask);
-		d->cbm[msr_param.low] = r->tmp_cbms[idx++];
+		if (d->cbm[msr_param.low] != r->tmp_cbms[idx]) {
+			cpumask_set_cpu(cpumask_any(&d->cpu_mask), cpu_mask);
+			d->cbm[msr_param.low] = r->tmp_cbms[idx];
+		}
+		idx++;
 	}
 	cpu = get_cpu();
 	/* Update CBM on this cpu if it's in cpu_mask. */
-- 
1.9.1