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authorAdhemerval Zanella <adhemerval.zanella@linaro.org>2017-01-31 18:01:59 -0200
committerAdhemerval Zanella <adhemerval.zanella@linaro.org>2017-06-14 17:22:35 -0300
commit0edbf1230131dfeb03d843d2859e2104456fad80 (patch)
tree308321439470d11d70f6b84464d33021cf65f575 /benchtests
parent5c3e322d3be3803636e38bcaf083fb59b3a34f0c (diff)
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nptl: Invert the mmap/mprotect logic on allocated stacks (BZ#18988)
Current allocate_stack logic for create stacks is to first mmap all the required memory with the desirable memory and then mprotect the guard area with PROT_NONE if required. Although it works as expected, it pessimizes the allocation because it requires the kernel to actually increase commit charge (it counts against the available physical/swap memory available for the system). The only issue is to actually check this change since side-effects are really Linux specific and to actually account them it would require a kernel specific tests to parse the system wide information. On the kernel I checked /proc/self/statm does not show any meaningful difference for vmm and/or rss before and after thread creation. I could only see really meaningful information checking on system wide /proc/meminfo between thread creation: MemFree, MemAvailable, and Committed_AS shows large difference without the patch. I think trying to use these kind of information on a testcase is fragile. The BZ#18988 reports shows that the commit pages are easily seen with mlockall (MCL_FUTURE) (with lock all pages that become mapped in the process) however a more straighfoward testcase shows that pthread_create could be faster using this patch: -- static const int inner_count = 256; static const int outer_count = 128; static void *thread1(void *arg) { return NULL; } static void *sleeper(void *arg) { pthread_t ts[inner_count]; for (int i = 0; i < inner_count; i++) pthread_create (&ts[i], &a, thread1, NULL); for (int i = 0; i < inner_count; i++) pthread_join (ts[i], NULL); return NULL; } int main(void) { pthread_attr_init(&a); pthread_attr_setguardsize(&a, 1<<20); pthread_attr_setstacksize(&a, 1134592); pthread_t ts[outer_count]; for (int i = 0; i < outer_count; i++) pthread_create(&ts[i], &a, sleeper, NULL); for (int i = 0; i < outer_count; i++) pthread_join(ts[i], NULL); assert(r == 0); } return 0; } -- On x86_64 (4.4.0-45-generic, gcc 5.4.0) running the small benchtests I see: $ time ./test real 0m3.647s user 0m0.080s sys 0m11.836s While with the patch I see: $ time ./test real 0m0.696s user 0m0.040s sys 0m1.152s So I added a pthread_create benchtest (thread_create) which check the thread creation latency. As for the simple benchtests, I saw improvements in thread creation on all architectures I tested the change. Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu, arm-linux-gnueabihf, powerpc64le-linux-gnu, sparc64-linux-gnu, and sparcv9-linux-gnu. [BZ #18988] * benchtests/thread_create-inputs: New file. * benchtests/thread_create-source.c: Likewise. * support/xpthread_attr_setguardsize.c: Likewise. * support/Makefile (libsupport-routines): Add xpthread_attr_setguardsize object. * support/xthread.h: Add xpthread_attr_setguardsize prototype. * benchtests/Makefile (bench-pthread): Add thread_create. * nptl/allocatestack.c (allocate_stack): Call mmap with PROT_NONE and then mprotect the required area.
Diffstat (limited to 'benchtests')
-rw-r--r--benchtests/Makefile2
-rw-r--r--benchtests/thread_create-inputs14
-rw-r--r--benchtests/thread_create-source.c58
3 files changed, 73 insertions, 1 deletions
diff --git a/benchtests/Makefile b/benchtests/Makefile
index 7f5fda5ef4..1e28e87919 100644
--- a/benchtests/Makefile
+++ b/benchtests/Makefile
@@ -25,7 +25,7 @@ bench-math := acos acosh asin asinh atan atanh cos cosh exp exp2 log log2 \
modf pow rint sin sincos sinh sqrt tan tanh fmin fmax fminf \
fmaxf
-bench-pthread := pthread_once
+bench-pthread := pthread_once thread_create
bench-string := ffs ffsll
diff --git a/benchtests/thread_create-inputs b/benchtests/thread_create-inputs
new file mode 100644
index 0000000000..e3ca03b0da
--- /dev/null
+++ b/benchtests/thread_create-inputs
@@ -0,0 +1,14 @@
+## args: int:size_t:size_t
+## init: thread_create_init
+## includes: pthread.h
+## include-sources: thread_create-source.c
+
+## name: stack=1024,guard=1
+32, 1024, 1
+## name: stack=1024,guard=2
+32, 1024, 2
+
+## name: stack=2048,guard=1
+32, 2048, 1
+## name: stack=2048,guard=2
+32, 2048, 2
diff --git a/benchtests/thread_create-source.c b/benchtests/thread_create-source.c
new file mode 100644
index 0000000000..035894a63b
--- /dev/null
+++ b/benchtests/thread_create-source.c
@@ -0,0 +1,58 @@
+/* Measure pthread_create thread creation with different stack
+ and guard sizes.
+
+ Copyright (C) 2017 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 <stdio.h>
+#include <unistd.h>
+#include <support/xthread.h>
+
+static size_t pgsize;
+
+static void
+thread_create_init (void)
+{
+ pgsize = sysconf (_SC_PAGESIZE);
+}
+
+static void *
+thread_dummy (void *arg)
+{
+ return NULL;
+}
+
+static void
+thread_create (int nthreads, size_t stacksize, size_t guardsize)
+{
+ pthread_attr_t attr;
+ xpthread_attr_init (&attr);
+
+ stacksize = stacksize * pgsize;
+ guardsize = guardsize * pgsize;
+
+ xpthread_attr_setstacksize (&attr, stacksize);
+ xpthread_attr_setguardsize (&attr, guardsize);
+
+ pthread_t ts[nthreads];
+
+ for (int i = 0; i < nthreads; i++)
+ ts[i] = xpthread_create (&attr, thread_dummy, NULL);
+
+ for (int i = 0; i < nthreads; i++)
+ xpthread_join (ts[i]);
+}