Re: PR/49816 CVS commit: src/libexec/ld.elf_so

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

The following reply was made to PR lib/49816; it has been noted by GNATS.

From: Joerg Sonnenberger <joerg%britannica.bec.de@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: PR/49816 CVS commit: src/libexec/ld.elf_so
Date: Mon, 6 Apr 2015 20:16:22 +0200

 On Mon, Apr 06, 2015 at 04:45:01PM +0000, YAMAMOTO Takashi wrote:
 > The following reply was made to PR lib/49816; it has been noted by GNATS.
 > 
 > From: yamt%netbsd.org@localhost (YAMAMOTO Takashi)
 > To: gnats-bugs%NetBSD.org@localhost
 > Cc: lib-bug-people%netbsd.org@localhost, gnats-admin%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost,
 > 	yamt%NetBSD.org@localhost
 > Subject: Re: PR/49816 CVS commit: src/libexec/ld.elf_so
 > Date: Mon,  6 Apr 2015 16:41:01 +0000 (UTC)
 > 
 >  > The following reply was made to PR lib/49816; it has been noted by GNATS.
 >  > 
 >  > From: Joerg Sonnenberger <joerg%britannica.bec.de@localhost>
 >  > To: gnats-bugs%NetBSD.org@localhost
 >  > Cc: lib-bug-people%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
 >  > 	netbsd-bugs%netbsd.org@localhost, yamt%NetBSD.org@localhost
 >  > Subject: Re: PR/49816 CVS commit: src/libexec/ld.elf_so
 >  > Date: Mon, 6 Apr 2015 18:22:21 +0200
 >  > 
 >  >  On Mon, Apr 06, 2015 at 04:10:02PM +0000, YAMAMOTO Takashi wrote:
 >  >  >  except that:
 >  >  >  * _rtld_exclusive_exit doesn't use CAS
 >  >  >  * this code is MI
 >  >  >  
 >  >  >  i agree that something like PTHREAD__ATOMIC_IS_MEMBAR
 >  >  >  would be a nice optimization, though.
 >  >  
 >  >  So which platform are you worried about that doesn't have TSO and
 >  >  doesn't implicit membars for CAS? I'm asking because the only reason
 >  >  those changes should help your problem is if they massively penalize the
 >  >  operation.
 >  
 >  well, can you explain why _rtld_exclusive_exit is safe
 >  without cas or barrier?
 
 All sane MP platforms at least implement Total Store Ordering. So all
 unrelated stores are visible no later than the reset of the mutex.
 That's why I am surprised that it changes anything at all for you.
 
 Joerg