Messages in this thread | | | From | KY Srinivasan <> | Subject | RE: [PATCH -tip 00/12] locking/atomics: Add and use inc,dec calls for FETCH-OP flavors | Date | Fri, 24 Jun 2016 17:45:32 +0000 |
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> -----Original Message----- > From: Davidlohr Bueso [mailto:dave@stgolabs.net] > Sent: Friday, June 24, 2016 10:30 AM > To: James Bottomley <James.Bottomley@HansenPartnership.com> > Cc: peterz@infradead.org; mingo@kernel.org; davem@davemloft.net; > cw00.choi@samsung.com; dougthompson@xmission.com; bp@alien8.de; > mchehab@osg.samsung.com; gregkh@linuxfoundation.org; pfg@sgi.com; > jikos@kernel.org; hans.verkuil@cisco.com; awalls@md.metrocast.net; > dledford@redhat.com; sean.hefty@intel.com; KY Srinivasan > <kys@microsoft.com>; heiko.carstens@de.ibm.com; > sumit.semwal@linaro.org; schwidefsky@de.ibm.com; linux- > kernel@vger.kernel.org > 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
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