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.