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Re: [PATCH] x86: Use RTM intrinsics in pthread mutex lock elision



On 02/10/2018 10:49, H.J. Lu wrote:
> On Tue, Oct 2, 2018 at 6:06 AM Adhemerval Zanella
> <adhemerval.zanella@linaro.org> wrote:
>>
>>
>>
>> On 01/10/2018 19:08, H.J. Lu wrote:
>>> Since RTM intrinsics are supported in GCC 4.9, we can use them in
>>> pthread mutex lock elision.
>>>
>>>       * sysdeps/unix/sysv/linux/x86/Makefile (CFLAGS-elision-lock.c):
>>>       Add -mrtm.
>>>       (CFLAGS-elision-unlock.c): Likewise.
>>>       (CFLAGS-elision-timed.c): Likewise.
>>>       (CFLAGS-elision-trylock.c): Likewise.
>>>       * sysdeps/unix/sysv/linux/x86/hle.h: Rewritten.
>>
>> LGTM, thanks.
>>
>>> ---
>>>  sysdeps/unix/sysv/linux/x86/Makefile |  4 ++
>>>  sysdeps/unix/sysv/linux/x86/hle.h    | 70 ++--------------------------
>>>  2 files changed, 7 insertions(+), 67 deletions(-)
>>>
>>> diff --git a/sysdeps/unix/sysv/linux/x86/Makefile b/sysdeps/unix/sysv/linux/x86/Makefile
>>> index 7dc4e61756..02ca36c6d2 100644
>>> --- a/sysdeps/unix/sysv/linux/x86/Makefile
>>> +++ b/sysdeps/unix/sysv/linux/x86/Makefile
>>> @@ -14,6 +14,10 @@ endif
>>>  ifeq ($(subdir),nptl)
>>>  libpthread-sysdep_routines += elision-lock elision-unlock elision-timed \
>>>                             elision-trylock
>>> +CFLAGS-elision-lock.c += -mrtm
>>> +CFLAGS-elision-unlock.c += -mrtm
>>> +CFLAGS-elision-timed.c += -mrtm
>>> +CFLAGS-elision-trylock.c += -mrtm
>>>  endif
>>>
>>>  ifeq ($(subdir),elf)
>>> diff --git a/sysdeps/unix/sysv/linux/x86/hle.h b/sysdeps/unix/sysv/linux/x86/hle.h
>>> index 4a7b9e3bf7..0449026839 100644
>>> --- a/sysdeps/unix/sysv/linux/x86/hle.h
>>> +++ b/sysdeps/unix/sysv/linux/x86/hle.h
>>> @@ -1,75 +1,11 @@
>>> -/* Shared RTM header.  Emulate TSX intrinsics for compilers and assemblers
>>> -   that do not support the intrinsics and instructions yet.  */
>>> +/* Shared RTM header.  */
>>>  #ifndef _HLE_H
>>>  #define _HLE_H 1
>>>
>>> -#ifdef __ASSEMBLER__
>>> +#include <x86intrin.h>
>>
>> Is it used in any configuration in assembly code?
> 
> No:
> 
> sysdeps/unix/sysv/linux/x86/elision-lock.c:#include "hle.h"
> sysdeps/unix/sysv/linux/x86/elision-trylock.c:#include "hle.h"
> sysdeps/unix/sysv/linux/x86/elision-unlock.c:#include "hle.h"
> sysdeps/x86/elide.h:#include <hle.h>
> 
> BTW, elide.h isn't used anywhere.
> 

It was used by HTM lock elision on pthread_rwlock_* before new implementation
(cc25c8b4c1196a8c29e9a45b1e096b99a87b7f8c).  Andrew Senkevich has sent a 
patch [1] to re-enable HTM rwlock elision, but his own performance results
seem mixed.

I think we can safely remove all elide.h files from now.

[1] https://sourceware.org/ml/libc-alpha/2017-04/msg00067.html


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