| Message ID | 9aca1f7c-e7eb-e101-249e-8b5edd21cd48@suse.cz |
|---|---|
| State | New |
| Headers | show |
On 10/04/2016 06:05 AM, Martin Liška wrote: > On 10/03/2016 02:26 PM, Nathan Sidwell wrote: >> > On 10/03/16 08:13, Martin Liška wrote: >>> >> On 08/18/2016 05:53 PM, Jeff Law wrote: >>>> >>> On 08/18/2016 09:51 AM, Andi Kleen wrote: >>>>>> >>>>> I'd prefer to make updates atomic in multi-threaded applications. >>>>>> >>>>> The best proxy we have for that is -pthread. >>>>>> >>>>> >>>>>> >>>>> Is it slower, most definitely, but odds are we're giving folks >>>>>> >>>>> garbage data otherwise, which in many ways is even worse. >>>>> >>>> >>>>> >>>> It will likely be catastrophically slower in some cases. >>>>> >>>> >>>>> >>>> Catastrophically as in too slow to be usable. >>>>> >>>> >>>>> >>>> An atomic instruction is a lot more expensive than a single increment. Also >>>>> >>>> they sometimes are really slow depending on the state of the machine. >>>> >>> And for those cases there's a way to override. >>>> >>> >>>> >>> The default should be set for correctness. >>>> >>> >>>> >>> jeff >>> >> >>> >> I would to somehow resolve the discussion related to default value selection. >>> >> Is the prevailing consensus that we should set -fprofile-update=atomic when >>> >> -pthread is set? If so, I'll prepare a patch. I tend to do it this way. >> > >> > This is my preference. >> > >> > nathan > Ok, this is final version of patch which implements both the warning and appending -fprofile-update > to a command line options. > > Patch can bootstrap on ppc64le-redhat-linux and survives regression tests. > > Ready to be installed? > Martin > > > 0001-Add-fprofile-update-option-juggling.patch > > > From 343d64a3c6b515053459a8ece6f9b0ad6ce86273 Mon Sep 17 00:00:00 2001 > From: marxin <mliska@suse.cz> > Date: Tue, 4 Oct 2016 10:46:48 +0200 > Subject: [PATCH] Add -fprofile-update option juggling > > gcc/ChangeLog: > > 2016-10-04 Martin Liska <mliska@suse.cz> > > * gcc.c: Set -fprofile-update=atomic when profiling is > enabled and -pthread is set. Warn when one combines > -pthread and -fprofile-update=single for an app using > profiling code. OK. jeff
From 343d64a3c6b515053459a8ece6f9b0ad6ce86273 Mon Sep 17 00:00:00 2001 From: marxin <mliska@suse.cz> Date: Tue, 4 Oct 2016 10:46:48 +0200 Subject: [PATCH] Add -fprofile-update option juggling gcc/ChangeLog: 2016-10-04 Martin Liska <mliska@suse.cz> * gcc.c: Set -fprofile-update=atomic when profiling is enabled and -pthread is set. Warn when one combines -pthread and -fprofile-update=single for an app using profiling code. --- gcc/gcc.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/gcc/gcc.c b/gcc/gcc.c index fd2b182..5213cb0 100644 --- a/gcc/gcc.c +++ b/gcc/gcc.c @@ -1141,7 +1141,14 @@ static const char *cc1_options = %{-help=*:--help=%*}\ %{!fsyntax-only:%{S:%W{o*}%{!o*:-o %b.s}}}\ %{fsyntax-only:-o %j} %{-param*}\ - %{coverage:-fprofile-arcs -ftest-coverage}"; + %{coverage:-fprofile-arcs -ftest-coverage}\ + %{fprofile-arcs|fprofile-generate*|coverage:\ + %{!fprofile-update=single:\ + %{pthread:-fprofile-update=atomic}}}\ + %{fprofile-update=single:\ + %{fprofile-arcs|fprofile-generate*|coverage:\ + %{pthread:%n-fprofile-update=atomic should be used\ + for a multithreaded application}}}"; static const char *asm_options = "%{-target-help:%:print-asm-header()} " -- 2.9.2