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From: Davidlohr Bueso <dave@stgolabs.net>
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, 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
Date: Fri, 24 Jun 2016 10:30:28 -0700	[thread overview]
Message-ID: <20160624173028.GA24658@linux-80c1.suse> (raw)
In-Reply-To: <1466786765.2343.37.camel@HansenPartnership.com>

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
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://lkml.org/lkml/2016/3/15/352.

Thanks,
Davidlohr

  reply	other threads:[~2016-06-24 17:30 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-20 20:05 [PATCH -tip 00/12] locking/atomics: Add and use inc,dec calls for FETCH-OP flavors Davidlohr Bueso
2016-06-20 20:05 ` [PATCH 01/12] locking/atomic: Introduce inc/dec " Davidlohr Bueso
2016-06-21  7:28   ` Peter Zijlstra
2016-06-21 13:33   ` [PATCH v2 " Davidlohr Bueso
2016-06-21 16:36     ` Davidlohr Bueso
2016-06-23  9:09       ` Peter Zijlstra
2016-06-24 16:34         ` Davidlohr Bueso
2016-06-24 18:48           ` Peter Zijlstra
2016-06-28 21:56             ` [PATCH -v4 " Davidlohr Bueso
2016-07-07  8:33               ` [tip:locking/core] locking/atomic: Introduce inc/dec variants for the atomic_fetch_$op() API tip-bot for Davidlohr Bueso
2016-06-20 20:05 ` [PATCH 02/12] net/neighbour: Employ atomic_fetch_inc() Davidlohr Bueso
2016-06-20 20:05 ` [PATCH 03/12] PM,devfreq: " Davidlohr Bueso
2016-07-02  5:04   ` Chanwoo Choi
2016-06-20 20:05 ` [PATCH 04/12] EDAC: " Davidlohr Bueso
2016-06-21 13:59   ` Borislav Petkov
2016-06-20 20:05 ` [PATCH 05/12] tty/serial: " Davidlohr Bueso
2016-06-20 20:05 ` [PATCH 06/12] HID,wacom: " Davidlohr Bueso
2016-06-22  8:10   ` Jiri Kosina
2016-06-20 20:05 ` [PATCH 07/12] drivers/media: " Davidlohr Bueso
2016-07-13 16:07   ` Mauro Carvalho Chehab
2016-06-20 20:06 ` [PATCH 08/12] infiniband: " Davidlohr Bueso
2016-06-20 20:06 ` [PATCH 09/12] drivers/hv: " Davidlohr Bueso
2016-06-20 20:06 ` [PATCH 10/12] s390/scm_block: " Davidlohr Bueso
2016-06-20 20:06 ` [PATCH 11/12] scsi: " Davidlohr Bueso
2016-06-20 20:06 ` [PATCH 12/12] dma-buf/fence: Employ atomic_fetch_add Davidlohr Bueso
2016-06-24 16:46 ` [PATCH -tip 00/12] locking/atomics: Add and use inc,dec calls for FETCH-OP flavors James Bottomley
2016-06-24 17:30   ` Davidlohr Bueso [this message]
2016-06-24 17:44     ` James Bottomley
2016-06-24 20:35       ` Davidlohr Bueso
2016-06-24 17:45     ` KY Srinivasan
2016-06-24 19:35       ` Davidlohr Bueso
2016-06-24 19:17   ` Peter Zijlstra

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