glibc/backport-x86-Disable-non-temporal-memset-on-Skylake-Server.patch

From ce7c6c491ed0750a10f9a52b5edc710d978e70e2 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Mon, 15 Jul 2024 16:19:17 +0800
Subject: [PATCH 07/10] x86: Disable non-temporal memset on Skylake Server

The original commit enabling non-temporal memset on Skylake Server had
erroneous benchmarks (actually done on ICX).

Further benchmarks indicate non-temporal stores may in fact by a
regression on Skylake Server.

This commit may be over-cautious in some cases, but should avoid any
regressions for 2.40.

Tested using qemu on all x86_64 cpu arch supported by both qemu +
GLIBC.

Reviewed-by: DJ Delorie <dj@redhat.com>
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
---
 sysdeps/x86/cpu-features.c                    |  13 +-
 sysdeps/x86/cpu-tunables.c                    |   6 +
 sysdeps/x86/dl-cacheinfo.h                    |  15 +-
 ...cpu-features-preferred_feature_index_1.def |   1 +
 sysdeps/x86/tst-hwcap-tunables.c              | 148 ++++++++++++++++++
 5 files changed, 173 insertions(+), 10 deletions(-)
 create mode 100644 sysdeps/x86/tst-hwcap-tunables.c

diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index c4dd85145e..b4030776a7 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -754,11 +754,18 @@ init_cpu_features (struct cpu_features *cpu_features)
 
 	      /* Newer Bigcore microarch (larger non-temporal store
 		 threshold).  */
-	    case INTEL_BIGCORE_SKYLAKE:
-	    case INTEL_BIGCORE_KABYLAKE:
-	    case INTEL_BIGCORE_COMETLAKE:
 	    case INTEL_BIGCORE_SKYLAKE_AVX512:
 	    case INTEL_BIGCORE_CANNONLAKE:
+	      /* Benchmarks indicate non-temporal memset is not
+		     necessarily profitable on SKX (and in some cases much
+		     worse). This is likely unique to SKX due its it unique
+		     mesh interconnect (not present on ICX or BWD). Disable
+		     non-temporal on all Skylake servers. */
+	      cpu_features->preferred[index_arch_Avoid_Non_Temporal_Memset]
+		  |= bit_arch_Avoid_Non_Temporal_Memset;
+	    case INTEL_BIGCORE_COMETLAKE:
+	    case INTEL_BIGCORE_SKYLAKE:
+	    case INTEL_BIGCORE_KABYLAKE:
 	    case INTEL_BIGCORE_ICELAKE:
 	    case INTEL_BIGCORE_TIGERLAKE:
 	    case INTEL_BIGCORE_ROCKETLAKE:
diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c
index 0d4f328585..b8475730ea 100644
--- a/sysdeps/x86/cpu-tunables.c
+++ b/sysdeps/x86/cpu-tunables.c
@@ -272,6 +272,12 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
 		 disable, 24);
 	    }
 	  break;
+	case 25:
+	  {
+	    CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
+				              Avoid_Non_Temporal_Memset,
+						      disable, 25);
+	  }
 	case 26:
 	    {
 	      CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h
index a76df092e6..de4584116f 100644
--- a/sysdeps/x86/dl-cacheinfo.h
+++ b/sysdeps/x86/dl-cacheinfo.h
@@ -1051,13 +1051,14 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
   /* Non-temporal stores are more performant on Intel and AMD hardware above
      non_temporal_threshold. Enable this for both Intel and AMD hardware. */
   unsigned long int memset_non_temporal_threshold = SIZE_MAX;
-  if (cpu_features->basic.kind == arch_kind_intel
-      || cpu_features->basic.kind == arch_kind_amd)
-      memset_non_temporal_threshold = non_temporal_threshold;
-
-   /* For AMD CPUs that support ERMS (Zen3+), REP MOVSB is in a lot of
-      cases slower than the vectorized path (and for some alignments,
-      it is really slow, check BZ #30994).  */
+  if (!CPU_FEATURES_ARCH_P (cpu_features, Avoid_Non_Temporal_Memset)
+      && (cpu_features->basic.kind == arch_kind_intel
+	  || cpu_features->basic.kind == arch_kind_amd))
+    memset_non_temporal_threshold = non_temporal_threshold;
+
+  /* For AMD CPUs that support ERMS (Zen3+), REP MOVSB is in a lot of
+     cases slower than the vectorized path (and for some alignments,
+     it is really slow, check BZ #30994).  */
   if (cpu_features->basic.kind == arch_kind_amd)
     rep_movsb_threshold = non_temporal_threshold;
 
diff --git a/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def b/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def
index d20c5b3196..aae1c85551 100644
--- a/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def
+++ b/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def
@@ -33,3 +33,4 @@ BIT (Prefer_No_AVX512)
 BIT (MathVec_Prefer_No_AVX512)
 BIT (Prefer_FSRM)
 BIT (Avoid_Short_Distance_REP_MOVSB)
+BIT (Avoid_Non_Temporal_Memset)
diff --git a/sysdeps/x86/tst-hwcap-tunables.c b/sysdeps/x86/tst-hwcap-tunables.c
new file mode 100644
index 0000000000..94307283d7
--- /dev/null
+++ b/sysdeps/x86/tst-hwcap-tunables.c
@@ -0,0 +1,148 @@
+/* Tests for x86 GLIBC_TUNABLES=glibc.cpu.hwcaps filter.
+   Copyright (C) 2023-2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <array_length.h>
+#include <getopt.h>
+#include <ifunc-impl-list.h>
+#include <spawn.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <intprops.h>
+#include <support/check.h>
+#include <support/support.h>
+#include <support/xunistd.h>
+#include <support/capture_subprocess.h>
+
+/* Nonzero if the program gets called via `exec'.  */
+#define CMDLINE_OPTIONS \
+  { "restart", no_argument, &restart, 1 },
+static int restart;
+
+/* Disable everything.  */
+static const char *test_1[] =
+{
+  "__memcpy_avx512_no_vzeroupper",
+  "__memcpy_avx512_unaligned",
+  "__memcpy_avx512_unaligned_erms",
+  "__memcpy_evex_unaligned",
+  "__memcpy_evex_unaligned_erms",
+  "__memcpy_avx_unaligned",
+  "__memcpy_avx_unaligned_erms",
+  "__memcpy_avx_unaligned_rtm",
+  "__memcpy_avx_unaligned_erms_rtm",
+  "__memcpy_ssse3",
+};
+
+static const struct test_t
+{
+  const char *env;
+  const char *const *funcs;
+  size_t nfuncs;
+} tests[] =
+{
+  {
+    /* Disable everything.  */
+    "-Prefer_ERMS,-Prefer_FSRM,-AVX,-AVX2,-AVX512F,-AVX512VL,"
+    "-SSE4_1,-SSE4_2,-SSSE3,-Fast_Unaligned_Load,-ERMS,"
+    "-AVX_Fast_Unaligned_Load,-Avoid_Non_Temporal_Memset",
+    test_1,
+    array_length (test_1)
+  },
+  {
+    /* Same as before, but with some empty suboptions.  */
+    ",-,-Prefer_ERMS,-Prefer_FSRM,-AVX,-AVX2,-AVX512F,-AVX512VL,"
+    "-SSE4_1,-SSE4_2,-SSSE3,-Fast_Unaligned_Load,,-,"
+    "-ERMS,-AVX_Fast_Unaligned_Load,-Avoid_Non_Temporal_Memset,-,",
+    test_1,
+    array_length (test_1)
+  }
+};
+
+/* Called on process re-execution.  */
+_Noreturn static void
+handle_restart (int ntest)
+{
+  struct libc_ifunc_impl impls[32];
+  int cnt = __libc_ifunc_impl_list ("memcpy", impls, array_length (impls));
+  if (cnt == 0)
+    _exit (EXIT_SUCCESS);
+  TEST_VERIFY_EXIT (cnt >= 1);
+  for (int i = 0; i < cnt; i++)
+    {
+      for (int f = 0; f < tests[ntest].nfuncs; f++)
+	{
+	  if (strcmp (impls[i].name, tests[ntest].funcs[f]) == 0)
+	    TEST_COMPARE (impls[i].usable, false);
+	}
+    }
+
+  _exit (EXIT_SUCCESS);
+}
+
+static int
+do_test (int argc, char *argv[])
+{
+  /* We must have either:
+     - One our fource parameters left if called initially:
+       + path to ld.so         optional
+       + "--library-path"      optional
+       + the library path      optional
+       + the application name
+       + the test to check  */
+
+  TEST_VERIFY_EXIT (argc == 2 || argc == 5);
+
+  if (restart)
+    handle_restart (atoi (argv[1]));
+
+  char nteststr[INT_BUFSIZE_BOUND (int)];
+
+  char *spargv[10];
+  {
+    int i = 0;
+    for (; i < argc - 1; i++)
+      spargv[i] = argv[i + 1];
+    spargv[i++] = (char *) "--direct";
+    spargv[i++] = (char *) "--restart";
+    spargv[i++] = nteststr;
+    spargv[i] = NULL;
+  }
+
+  for (int i = 0; i < array_length (tests); i++)
+    {
+      snprintf (nteststr, sizeof nteststr, "%d", i);
+
+      printf ("[%d] Spawned test for %s\n", i, tests[i].env);
+      char *tunable = xasprintf ("glibc.cpu.hwcaps=%s", tests[i].env);
+      setenv ("GLIBC_TUNABLES", tunable, 1);
+
+      struct support_capture_subprocess result
+	= support_capture_subprogram (spargv[0], spargv, NULL);
+      support_capture_subprocess_check (&result, "tst-tunables", 0,
+					sc_allow_stderr);
+      support_capture_subprocess_free (&result);
+
+      free (tunable);
+    }
+
+  return 0;
+}
+
+#define TEST_FUNCTION_ARGV do_test
+#include <support/test-driver.c>
-- 
2.17.1