From f98a2768ca0609fb81a0ee8f30ac1e70269334c4 Mon Sep 17 00:00:00 2001 From: Timothy Arceri Date: Mon, 16 Oct 2017 18:06:49 +1100 Subject: [PATCH] mesa: Add new fast mtx_t mutex type for basic use cases MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit While modern pthread mutexes are very fast, they still incur a call to an external DSO and overhead of the generality and features of pthread mutexes. Most mutexes in mesa only needs lock/unlock, and the idea here is that we can inline the atomic operation and make the fast case just two intructions. Mutexes are subtle and finicky to implement, so we carefully copy the implementation from Ulrich Dreppers well-written and well-reviewed paper: "Futexes Are Tricky" http://www.akkadia.org/drepper/futex.pdf We implement "mutex3", which gives us a mutex that has no syscalls on uncontended lock or unlock. Further, the uncontended case boils down to a cmpxchg and an untaken branch and the uncontended unlock is just a locked decr and an untaken branch. We use __builtin_expect() to indicate that contention is unlikely so that gcc will put the contention code out of the main code flow. A fast mutex only supports lock/unlock, can't be recursive or used with condition variables. We keep the pthread mutex implementation around as for the few places where we use condition variables or recursive locking. For platforms or compilers where futex and atomics aren't available, simple_mtx_t falls back to the pthread mutex. The pthread mutex lock/unlock overhead shows up on benchmarks for CPU bound applications. Most CPU bound cases are helped and some of our internal bind_buffer_object heavy benchmarks gain up to 10%. Signed-off-by: Kristian Høgsberg Signed-off-by: Timothy Arceri Reviewed-by: Nicolai Hähnle --- configure.ac | 3 + meson.build | 2 +- src/intel/vulkan/anv_allocator.c | 24 +----- src/util/Makefile.sources | 1 + src/util/meson.build | 1 + src/util/simple_mtx.h | 155 +++++++++++++++++++++++++++++++++++++++ 6 files changed, 162 insertions(+), 24 deletions(-) create mode 100644 src/util/simple_mtx.h diff --git a/configure.ac b/configure.ac index d362dfb1..411c4f6 100644 --- a/configure.ac +++ b/configure.ac @@ -935,6 +935,9 @@ if test "x$pthread_stubs_possible" = xyes; then PKG_CHECK_MODULES(PTHREADSTUBS, pthread-stubs >= 0.4) fi +dnl Check for futex for fast inline simple_mtx_t. +AC_CHECK_HEADER([linux/futex.h], [DEFINES="$DEFINES -DHAVE_LINUX_FUTEX_H"]) + dnl SELinux awareness. AC_ARG_ENABLE([selinux], [AS_HELP_STRING([--enable-selinux], diff --git a/meson.build b/meson.build index cd70651..314d15a 100644 --- a/meson.build +++ b/meson.build @@ -528,7 +528,7 @@ elif cc.has_header_symbol('sys/mkdev.h', 'major') pre_args += '-DMAJOR_IN_MKDEV' endif -foreach h : ['xlocale.h', 'sys/sysctl.h'] +foreach h : ['xlocale.h', 'sys/sysctl.h', 'linux/futex.h'] if cc.has_header(h) pre_args += '-DHAVE_@0@'.format(h.to_upper().underscorify()) endif diff --git a/src/intel/vulkan/anv_allocator.c b/src/intel/vulkan/anv_allocator.c index 27eedb5..4d8eea6 100644 --- a/src/intel/vulkan/anv_allocator.c +++ b/src/intel/vulkan/anv_allocator.c @@ -21,20 +21,17 @@ * IN THE SOFTWARE. */ -#include #include #include #include #include -#include #include -#include #include -#include #include "anv_private.h" #include "util/hash_table.h" +#include "util/simple_mtx.h" #ifdef HAVE_VALGRIND #define VG_NOACCESS_READ(__ptr) ({ \ @@ -112,25 +109,6 @@ struct anv_mmap_cleanup { #define ANV_MMAP_CLEANUP_INIT ((struct anv_mmap_cleanup){0}) -static inline long -sys_futex(void *addr1, int op, int val1, - struct timespec *timeout, void *addr2, int val3) -{ - return syscall(SYS_futex, addr1, op, val1, timeout, addr2, val3); -} - -static inline int -futex_wake(uint32_t *addr, int count) -{ - return sys_futex(addr, FUTEX_WAKE, count, NULL, NULL, 0); -} - -static inline int -futex_wait(uint32_t *addr, int32_t value) -{ - return sys_futex(addr, FUTEX_WAIT, value, NULL, NULL, 0); -} - static inline int memfd_create(const char *name, unsigned int flags) { diff --git a/src/util/Makefile.sources b/src/util/Makefile.sources index c7f6516..9393f6a 100644 --- a/src/util/Makefile.sources +++ b/src/util/Makefile.sources @@ -35,6 +35,7 @@ MESA_UTIL_FILES := \ set.c \ set.h \ simple_list.h \ + simple_mtx.h \ slab.c \ slab.h \ string_buffer.c \ diff --git a/src/util/meson.build b/src/util/meson.build index c9cb3e8..0145d9c 100644 --- a/src/util/meson.build +++ b/src/util/meson.build @@ -59,6 +59,7 @@ files_mesa_util = files( 'set.c', 'set.h', 'simple_list.h', + 'simple_mtx.h', 'slab.c', 'slab.h', 'string_buffer.c', diff --git a/src/util/simple_mtx.h b/src/util/simple_mtx.h new file mode 100644 index 0000000..86ba026 --- /dev/null +++ b/src/util/simple_mtx.h @@ -0,0 +1,155 @@ +/* + * Copyright © 2015 Intel + * + * Permission is hereby granted, free of charge, to any person obtaining a + * copy of this software and associated documentation files (the "Software"), + * to deal in the Software without restriction, including without limitation + * the rights to use, copy, modify, merge, publish, distribute, sublicense, + * and/or sell copies of the Software, and to permit persons to whom the + * Software is furnished to do so, subject to the following conditions: + * + * The above copyright notice and this permission notice (including the next + * paragraph) shall be included in all copies or substantial portions of the + * Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS + * IN THE SOFTWARE. + */ + +#ifndef _SIMPLE_MTX_H +#define _SIMPLE_MTX_H + +#include "c11/threads.h" + +#if defined(__GNUC__) && defined(HAVE_LINUX_FUTEX_H) + +/* mtx_t - Fast, simple mutex + * + * While modern pthread mutexes are very fast (implemented using futex), they + * still incur a call to an external DSO and overhead of the generality and + * features of pthread mutexes. Most mutexes in mesa only needs lock/unlock, + * and the idea here is that we can inline the atomic operation and make the + * fast case just two intructions. Mutexes are subtle and finicky to + * implement, so we carefully copy the implementation from Ulrich Dreppers + * well-written and well-reviewed paper: + * + * "Futexes Are Tricky" + * http://www.akkadia.org/drepper/futex.pdf + * + * We implement "mutex3", which gives us a mutex that has no syscalls on + * uncontended lock or unlock. Further, the uncontended case boils down to a + * locked cmpxchg and an untaken branch, the uncontended unlock is just a + * locked decr and an untaken branch. We use __builtin_expect() to indicate + * that contention is unlikely so that gcc will put the contention code out of + * the main code flow. + * + * A fast mutex only supports lock/unlock, can't be recursive or used with + * condition variables. + */ + +typedef struct { + uint32_t val; +} simple_mtx_t; + +#define _SIMPLE_MTX_INITIALIZER_NP { 0 } + +#include +#include +#include +#include + +static inline long sys_futex(void *addr1, int op, int val1, + struct timespec *timeout, void *addr2, int val3) +{ + return syscall(SYS_futex, addr1, op, val1, timeout, addr2, val3); +} + +static inline int futex_wake(uint32_t *addr, int count) +{ + return sys_futex(addr, FUTEX_WAKE, count, NULL, NULL, 0); +} + +static inline int futex_wait(uint32_t *addr, int32_t value) +{ + return sys_futex(addr, FUTEX_WAIT, value, NULL, NULL, 0); +} + +static inline void +simple_mtx_init(simple_mtx_t *mtx, int type) +{ + assert(type == mtx_plain); + + mtx->val = 0; +} + +static inline void +simple_mtx_destroy(simple_mtx_t *mtx) +{ +} + +static inline void +simple_mtx_lock(simple_mtx_t *mtx) +{ + uint32_t c; + + c = __sync_val_compare_and_swap(&mtx->val, 0, 1); + if (__builtin_expect(c != 0, 0)) { + if (c != 2) + c = __sync_lock_test_and_set(&mtx->val, 2); + while (c != 0) { + futex_wait(&mtx->val, 2); + c = __sync_lock_test_and_set(&mtx->val, 2); + } + } +} + +static inline void +simple_mtx_unlock(simple_mtx_t *mtx) +{ + uint32_t c; + + c = __sync_fetch_and_sub(&mtx->val, 1); + if (__builtin_expect(c != 1, 0)) { + mtx->val = 0; + futex_wake(&mtx->val, 1); + } +} + +#else + +typedef mtx_t simple_mtx_t; + +#define _SIMPLE_MTX_INITIALIZER_NP _MTX_INITIALIZER_NP + +static inline void +simple_mtx_init(simple_mtx_t *mtx, int type) +{ + mtx_init(mtx, type); +} + +static inline void +simple_mtx_destroy(simple_mtx_t *mtx) +{ + mtx_destroy(mtx); +} + +static inline void +simple_mtx_lock(simple_mtx_t *mtx) +{ + mtx_lock(mtx); +} + +static inline void +simple_mtx_unlock(simple_mtx_t *mtx) +{ + mtx_unlock(mtx); +} + +#endif + +#endif -- 2.7.4