[Mesa-dev] [RFC 1/3] mesa: Add new fast mtx_t mutex type for basic use cases
Tapani Pälli
tapani.palli at intel.com
Tue Oct 10 11:28:04 UTC 2017
ok another one too ...
On 10/10/2017 01:03 PM, Tapani Pälli wrote:
> one error found below ..
>
> On 10/10/2017 05:45 AM, Timothy Arceri wrote:
>> 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
>> full_mtx_t for the few places where we use condition variables or
>> recursive
>> locking. For platforms or compilers where futex and atomics aren't
>> available,
>> 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 <krh at bitplanet.net>
>> Signed-off-by: Timothy Arceri <tarceri at itsqueeze.com>
>> ---
>> configure.ac | 3 ++
>> src/util/simple_mtx.h | 146
>> ++++++++++++++++++++++++++++++++++++++++++++++++++
>> 2 files changed, 149 insertions(+)
>> create mode 100644 src/util/simple_mtx.h
>>
>> diff --git a/configure.ac b/configure.ac
>> index 903a3979d4..47fe427d19 100644
>> --- a/configure.ac
>> +++ b/configure.ac
>> @@ -887,20 +887,23 @@ linux* | cygwin* | darwin* | solaris* | *-gnu* |
>> gnu*)
>> ;;
>> * )
>> pthread_stubs_possible="yes"
>> ;;
>> esac
>> 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_FUTEX"])
>> +
>> dnl SELinux awareness.
>> AC_ARG_ENABLE([selinux],
>> [AS_HELP_STRING([--enable-selinux],
>> [Build SELinux-aware Mesa @<:@default=disabled@:>@])],
>> [MESA_SELINUX="$enableval"],
>> [MESA_SELINUX=no])
>> if test "x$enable_selinux" = "xyes"; then
>> PKG_CHECK_MODULES([SELINUX], [libselinux], [],
>> [AC_CHECK_HEADER([selinux/selinux.h],[],
>> [AC_MSG_ERROR([SELinux headers not found])])
>> diff --git a/src/util/simple_mtx.h b/src/util/simple_mtx.h
>> new file mode 100644
>> index 0000000000..bd365ac237
>> --- /dev/null
>> +++ b/src/util/simple_mtx.h
>> @@ -0,0 +1,146 @@
>> +/*
>> + * 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.
>> + */
>> +
>> +#if defined(__GNUC__) && defined(HAVE_FUTEX)
>> +
>> +/* 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 <stdint.h>
>> +#include <values.h>
values.h is unnecessary (not used) and not available on Android, I
suggest to remove this include.
>> +#include <linux/futex.h>
>> +#include <sys/time.h>
>> +#include <sys/syscall.h>
>> +
>> +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) {
>> + return sys_futex(addr, FUTEX_WAKE, 1, 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);
>> + }
>> +}
>> +
>> +#else
>> +
>> +typedef simple_mtx_t mtx_t;
>
> should be
>
> 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
>>
> _______________________________________________
> mesa-dev mailing list
> mesa-dev at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
More information about the mesa-dev
mailing list