> -----Original Message----- > From: Davidlohr Bueso [mailto:[email protected]] > Sent: Friday, June 24, 2016 10:30 AM > To: James Bottomley <[email protected]> > Cc: [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; KY Srinivasan > <[email protected]>; [email protected]; > [email protected]; [email protected]; linux- > [email protected] > Subject: Re: [PATCH -tip 00/12] locking/atomics: Add and use inc,dec calls for > FETCH-OP flavors > > On Fri, 24 Jun 2016, James Bottomley wrote: > > >On Mon, 2016-06-20 at 13:05 -0700, Davidlohr Bueso wrote: > >> Hi, > >> > >> The series is really straightforward and based on Peter's work that > >> introduces[1] the atomic_fetch_$op machinery. Only patch 1 implements > >> the actual atomic_fetch_{inc,dec} calls based on > >> atomic_fetch_{add,sub}. > > > >Could I just ask why? atomic_inc_return(x) - 1 seems a reasonable > >thing to do to me. > > For one restoring the old state like that can be racy and looses the notion of > atomicity. The new family of atomic_fetch_$ops also better express the How so? Can you expand on the racy part. The subtraction is done on a local copy of the value.
K. Y > purpose of the call imo. Finally, the added machinery (considering it came > from > fetch_op() NOHZ needs), was mainly suggested by Linus (although yes, we > don't have users for all the calls): > https://na01.safelinks.protection.outlook.com/?url=https%3a%2f%2flkml.org% > 2flkml%2f2016%2f3%2f15%2f352&data=01%7c01%7ckys%40microsoft.com% > 7c5c7cfad67568440f6e2108d39c5546e0%7c72f988bf86f141af91ab2d7cd011 > db47%7c1&sdata=uZrdmvDCuTp%2bMNHAXzMPT68w%2bVGtvH2V99nUEBr6 > 1ro%3d. > > Thanks, > Davidlohr
