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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 /support
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 'support')
-rw-r--r--support/Makefile1
-rw-r--r--support/xpthread_attr_setguardsize.c26
-rw-r--r--support/xthread.h2
3 files changed, 29 insertions, 0 deletions
diff --git a/support/Makefile b/support/Makefile
index 20b0343..a2480cd 100644
--- a/support/Makefile
+++ b/support/Makefile
@@ -82,6 +82,7 @@ libsupport-routines = \
xpthread_attr_init \
xpthread_attr_setdetachstate \
xpthread_attr_setstacksize \
+ xpthread_attr_setguardsize \
xpthread_barrier_destroy \
xpthread_barrier_init \
xpthread_barrier_wait \
diff --git a/support/xpthread_attr_setguardsize.c b/support/xpthread_attr_setguardsize.c
new file mode 100644
index 0000000..35fed5d
--- /dev/null
+++ b/support/xpthread_attr_setguardsize.c
@@ -0,0 +1,26 @@
+/* pthread_attr_setguardsize with error checking.
+ 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 <support/xthread.h>
+
+void
+xpthread_attr_setguardsize (pthread_attr_t *attr, size_t guardsize)
+{
+ xpthread_check_return ("pthread_attr_setguardize",
+ pthread_attr_setguardsize (attr, guardsize));
+}
diff --git a/support/xthread.h b/support/xthread.h
index 6dd7e70..3552a73 100644
--- a/support/xthread.h
+++ b/support/xthread.h
@@ -67,6 +67,8 @@ void xpthread_attr_setdetachstate (pthread_attr_t *attr,
int detachstate);
void xpthread_attr_setstacksize (pthread_attr_t *attr,
size_t stacksize);
+void xpthread_attr_setguardsize (pthread_attr_t *attr,
+ size_t guardsize);
/* This function returns non-zero if pthread_barrier_wait returned
PTHREAD_BARRIER_SERIAL_THREAD. */