powerpc/paravirt: Use is_kvm_guest() in vcpu_is_preempted()

srikard · mpe · commit ca3f969dcb11 · 2020-12-04T01:01:22.000+11:00
If its a shared LPAR but not a KVM guest, then see if the vCPU is related to the calling vCPU. On PowerVM, only cores can be preempted. So if one vCPU is a non-preempted state, we can decipher that all other vCPUs sharing the same core are in non-preempted state. Performance results: $ perf stat -r 5 -a perf bench sched pipe -l 10000000 (lesser time is better) powerpc/next 35,107,951.20 msec cpu-clock # 255.898 CPUs utilized ( +- 0.31% ) 23,655,348 context-switches # 0.674 K/sec ( +- 3.72% ) 14,465 cpu-migrations # 0.000 K/sec ( +- 5.37% ) 82,463 page-faults # 0.002 K/sec ( +- 8.40% ) 1,127,182,328,206 cycles # 0.032 GHz ( +- 1.60% ) (66.67%) 78,587,300,622 stalled-cycles-frontend # 6.97% frontend cycles idle ( +- 0.08% ) (50.01%) 654,124,218,432 stalled-cycles-backend # 58.03% backend cycles idle ( +- 1.74% ) (50.01%) 834,013,059,242 instructions # 0.74 insn per cycle # 0.78 stalled cycles per insn ( +- 0.73% ) (66.67%) 132,911,454,387 branches # 3.786 M/sec ( +- 0.59% ) (50.00%) 2,890,882,143 branch-misses # 2.18% of all branches ( +- 0.46% ) (50.00%) 137.195 +- 0.419 seconds time elapsed ( +- 0.31% ) powerpc/next + patchset 29,981,702.64 msec cpu-clock # 255.881 CPUs utilized ( +- 1.30% ) 40,162,456 context-switches # 0.001 M/sec ( +- 0.01% ) 1,110 cpu-migrations # 0.000 K/sec ( +- 5.20% ) 62,616 page-faults # 0.002 K/sec ( +- 3.93% ) 1,430,030,626,037 cycles # 0.048 GHz ( +- 1.41% ) (66.67%) 83,202,707,288 stalled-cycles-frontend # 5.82% frontend cycles idle ( +- 0.75% ) (50.01%) 744,556,088,520 stalled-cycles-backend # 52.07% backend cycles idle ( +- 1.39% ) (50.01%) 940,138,418,674 instructions # 0.66 insn per cycle # 0.79 stalled cycles per insn ( +- 0.51% ) (66.67%) 146,452,852,283 branches # 4.885 M/sec ( +- 0.80% ) (50.00%) 3,237,743,996 branch-misses # 2.21% of all branches ( +- 1.18% ) (50.01%) 117.17 +- 1.52 seconds time elapsed ( +- 1.30% ) This is around 14.6% improvement in performance. Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Acked-by: Waiman Long <longman@redhat.com> [mpe: Fold in performance results from cover letter] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20201202050456.164005-5-srikar@linux.vnet.ibm.com
diff --git a/arch/powerpc/include/asm/paravirt.h b/arch/powerpc/include/asm/paravirt.h
@@ -10,6 +10,9 @@
 #endif
 
 #ifdef CONFIG_PPC_SPLPAR
+#include <asm/kvm_guest.h>
+#include <asm/cputhreads.h>
+
 DECLARE_STATIC_KEY_FALSE(shared_processor);
 
 static inline bool is_shared_processor(void)
@@ -74,6 +77,21 @@ static inline bool vcpu_is_preempted(int cpu)
 {
 	if (!is_shared_processor())
 		return false;
+
+#ifdef CONFIG_PPC_SPLPAR
+	if (!is_kvm_guest()) {
+		int first_cpu = cpu_first_thread_sibling(smp_processor_id());
+
+		/*
+		 * Preemption can only happen at core granularity. This CPU
+		 * is not preempted if one of the CPU of this core is not
+		 * preempted.
+		 */
+		if (cpu_first_thread_sibling(cpu) == first_cpu)
+			return false;
+	}
+#endif
+
 	if (yield_count_of(cpu) & 1)
 		return true;
 	return false;
