RFR: Enable NUMA by default

[Roman Kennke]

Yeah, please do it.

Roman


Am 16. Oktober 2018 09:52:18 MESZ schrieb Aleksey Shipilev <shade at redhat.com>:
>Patch:
>
>diff -r 34af82382067
>src/hotspot/share/gc/shenandoah/shenandoahArguments.cpp
>--- a/src/hotspot/share/gc/shenandoah/shenandoahArguments.cpp   Fri Oct
>12 14:05:44 2018 +0200
>+++ b/src/hotspot/share/gc/shenandoah/shenandoahArguments.cpp   Tue Oct
>16 09:27:42 2018 +0200
>@@ -72,4 +72,12 @@
>   }
>
>+  // Enable NUMA by default. While Shenandoah is not NUMA-aware,
>enabling NUMA makes
>+  // storage allocation code NUMA-aware, and NUMA interleaving makes
>the storage
>+  // allocated in consistent manner (interleaving) to minimize
>run-to-run variance.
>+  if (FLAG_IS_DEFAULT(UseNUMA)) {
>+    FLAG_SET_DEFAULT(UseNUMA, true);
>+    FLAG_SET_DEFAULT(UseNUMAInterleaving, true);
>+  }
>+
>   FLAG_SET_DEFAULT(ParallelGCThreads,
>                    Abstract_VM_Version::parallel_worker_threads());
>
>
>Backing story: UseNUMA tries to enable Hotspot infrastructure for NUMA,
>if available. It would turn
>off if NUMA is not supported (ForceNUMA does force it, but not
>UseNUMA). JEP 163 was targeting to
>enable it by default, but it is seemingly abandoned. ZGC does enable
>NUMA with the similar code as
>above. The difference for Shenandoah is that allocation code is not
>NUMA-aware, so we do the next
>best thing: interleaving all memory at once. (This can be simulated now
>with -Xms -Xmx
>-XX:+AlwaysPreTouch that pretouches all memory by all workers, but
>plain interleaving seems more
>precise).
>
>Performance tests on my TR 2950X running in NUMA mode shows significant
>run-to-run variance
>improvements on Compress, CryptoRsa, CryptoSignVerify, Derby, Serial
>and XmlValidation.
>The improvements are good: average goes up +5%. In CryptoRsa case,
>average goes up +20%, because
>variance is really bad in UMA mode there.
>
>Testing: tier3_gc_shenandoah (NUMA-enabled TR, UMA i7)
>
>Thanks,
>-Aleksey