[Mesa-dev] [PATCH v3] mesa: Add new fast mtx_t mutex type for basic use cases

[Nicolai Hähnle]

On 03.11.2017 14:23, Nicolai Hähnle wrote:
> What's the status of this?
> 
> On 16.10.2017 14:36, Emil Velikov wrote:
>> On 16 October 2017 at 08:06, Timothy Arceri <tarceri at itsqueeze.com> 
>> 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.
>>>
>> Worth using likely/unlikely macros from src/util/macros.h?
>>
>>>   configure.ac                     |   3 +
>>>   src/intel/vulkan/anv_allocator.c |  24 +-----
>>>   src/util/Makefile.sources        |   1 +
>>>   src/util/meson.build             |   1 +
>>>   src/util/simple_mtx.h            | 153 
>>> +++++++++++++++++++++++++++++++++++++++
>>>   5 files changed, 159 insertions(+), 23 deletions(-)
>>>   create mode 100644 src/util/simple_mtx.h
>>>
>>> diff --git a/configure.ac b/configure.ac
>>> index 62d33a1941c..c113e714638 100644
>>> --- a/configure.ac
>>> +++ b/configure.ac
>>> @@ -894,6 +894,9 @@ 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_FUTEX"])
>>> +
>> Dylan you might want a similar check for Meson?
>>
>>
>>> +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);
>>> +}
>> Coding style: please keep { on the next line.

For what it's worth, with this fixed and possible Meson build issues 
addressed, this patch as well as v2 of patches 2 & 3 are

Reviewed-by: Nicolai Hähnle <nicolai.haehnle at amd.com>


>>
>> -Emil
>> _______________________________________________
>> mesa-dev mailing list
>> mesa-dev at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>>
> 
> 


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