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--- documentation:technical_docs:performance [2019/11/25 21:21] – [Cisco or Linux] olivier
+++ documentation:technical_docs:performance [2019/12/27 00:18] – [Disabling Hyper Threading (HT)] olivier
@@ Line 110: / Line 110: @@
 ==== Disabling Hyper Threading (HT) ====
-By default, lot's of multi-queue NIC drivers create one queue per core.
+By default a multi-queue NIC drivers create one queue per core.
-But "logical" cores didn't help at all for managing interrupts generated by high speed NIC (this is not true on 13-head since [[https://svnweb.freebsd.org/base?view=revision&revision=354338|r354338]] and the new machdep.hyperthreading_intr_allowed that allow interrupts on HTT logical CPUs.
+But on older CPU (like Xeon E5-2650 V1) those logical cores didn't help at all for managing interrupts generated by high speed NIC (this is not true on 13-head since [[https://svnweb.freebsd.org/base?view=revision&revision=354338|r354338]] and the new machdep.hyperthreading_intr_allowed that allow interrupts on HTT logical CPUs.
 HT can be disabled with this command:
@@ Line 118: / Line 118: @@
 </code>
-Here is an example on a 8cores x hardware threads Intel CPU and 10G Chelsio NIC:
+Here is an example on a Xeon E5 2650 (8c,16t) and 10G Chelsio NIC where it improve performance by disabling HT:
 <code>
-x HT-enabled-8rxq(default).packets-per-seconds
+x HT-enabled-8rxq(default): inet packets-per-second forwarded
-+ HT-enabled-16rxq.packets-per-seconds
++ HT-enabled-16rxq: inet packets-per-second forwarded
-* HT-disabled.packets-per-seconds
+* HT-disabled-8rxq: inet packets-per-seconds forwarded
 +--------------------------------------------------------------------------+
 |                                                                        **|
@@ Line 145: / Line 145: @@
 </code>
-There is a benefit of about 24% to disable hyper threading.
+There is a benefit of about 24% to disable hyper threading on this old CPU.
+But here is another example where there is a benefit to kept it enabled (and with the NIC configured to uses all the treads) on Xeon E5 2650L (10c, 20t):
+<code>
+x HT on, 8q (default): inet4 packets-per-second forwarded
++ HT off, 8q: inet4 packets-per-second forwarded
+* HT on, 16q: inet4 packets-per-second forwarded
++--------------------------------------------------------------------------+
+|x x              ++                                                   *  *|
+|x xx            +++                                                 * *  *|
+||AM|            |A_|                                                |_MA_||
++--------------------------------------------------------------------------+
+    N           Min           Max        Median           Avg        Stddev
+x   5       4265579     4433699.5     4409249.5     4359580.3       81559.4
++   5       5257621       5443012       5372493     5372693.5     73316.243
+Difference at 95.0% confidence
+.01311e+06 +/- 113098
+.2388% +/- 2.94299%
+        (Student's t, pooled s = 77547.4)
+*   5       8566972       8917315     8734750.5     8769616.1     147186.74
+Difference at 95.0% confidence
+.41004e+06 +/- 173536
+.157% +/- 5.21388%
+        (Student's t, pooled s = 118987)
+</code>
 ==== fastforwarding ====