Adding upstream version 1:10.11.6.upstream/1%10.11.6upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 79 insertions, 0 deletions

diff --git a/mysys/my_cpu.c b/mysys/my_cpu.c
new file mode 100644
index 00000000..52500d78
--- /dev/null
+++ b/mysys/my_cpu.c
@@ -0,0 +1,79 @@
+/* Copyright (c) 2019, 2020, MariaDB Corporation.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 of the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
+
+#include <my_global.h>
+#include <my_cpu.h>
+#include <my_rdtsc.h>
+
+#ifdef HAVE_PAUSE_INSTRUCTION
+/** How many times to invoke PAUSE in a loop */
+unsigned my_cpu_relax_multiplier = 200;
+
+#define PAUSE4  MY_RELAX_CPU(); MY_RELAX_CPU(); MY_RELAX_CPU(); MY_RELAX_CPU()
+#define PAUSE16 PAUSE4; PAUSE4; PAUSE4; PAUSE4
+
+/**
+  Initialize my_cpu_relax_multiplier.
+
+  Determine the duration of a PAUSE instruction by running an
+  unrolled loop of 16 PAUSE instructions twice, and taking the
+  faster of the two runs. In this way, even if the execution is
+  interrupted by the operating system, it should be extremely
+  unlikely that both loops get interrupted.
+
+  On the Intel Skylake microarchitecture, the PAUSE instruction takes
+  around 140 clock cycles, while on earlier microarchitectures it could
+  be 10 clock cycles or less. Scale the PAUSE loop counter accordingly.
+
+  On a pre-Skylake Intel Xeon CPU E5-2630 v4 @ 2.20GHz running an AMD64
+  executable, the numbers would be between 172 and 220 when all the code
+  is inlined as follows:
+
+  rdtsc,mov,shl,or, 16*pause,
+  rdtsc,mov,shl,or, 16*pause,
+  rdtsc.
+
+  That would yield 11 to 14 cycles per PAUSE instruction even if we
+  (wrongly) ignore the overhead of the other instructions.
+
+  On a Skylake mobile processor Intel Core i7-6500U CPU @ 2.50GHz, the
+  numbers would range from 1896 to 2410 (or 1976 if taking the minimum
+  of two runs), yielding 118 to 151 (or 123) cycles per PAUSE instruction.
+
+  Let us define a threshold at roughly 30 cycles per PAUSE instruction,
+  and use a shorter delay if the PAUSE instruction takes longer than
+  that. In some AMD processors, the PAUSE instruction could take 40 or
+  50 cycles. Let us use a shorter delay multiplier for them as well.
+
+  The 1/2 scaling factor (200/100) was derived experimentally by
+  Steve Shaw from Intel and Sergey Vojtovich from MariaDB Foundation.
+  In an earlier experiment on MySQL code base, a 1/10 scaling factor
+  (200/20) seemed to work best.
+
+  The basic idea of the detection algorithm (run 16 PAUSE instructions
+  between RDTSC) was suggested by Mikhail Sinyavin from Intel.
+*/
+void my_cpu_init(void)
+{
+  ulonglong t0, t1, t2;
+  t0= my_timer_cycles();
+  PAUSE16;
+  t1= my_timer_cycles();
+  PAUSE16;
+  t2= my_timer_cycles();
+  if (t2 - t1 > 30 * 16 && t1 - t0 > 30 * 16)
+    my_cpu_relax_multiplier= 100;
+}
+#endif