From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mails.dpdk.org (mails.dpdk.org [217.70.189.124]) by inbox.dpdk.org (Postfix) with ESMTP id 68ED24280A; Wed, 22 Mar 2023 15:58:11 +0100 (CET) Received: from mails.dpdk.org (localhost [127.0.0.1]) by mails.dpdk.org (Postfix) with ESMTP id 00DAD40E09; Wed, 22 Mar 2023 15:58:11 +0100 (CET) Received: from smartserver.smartsharesystems.com (smartserver.smartsharesystems.com [77.243.40.215]) by mails.dpdk.org (Postfix) with ESMTP id 4627440A84 for ; Wed, 22 Mar 2023 15:58:10 +0100 (CET) Content-class: urn:content-classes:message Subject: RE: [PATCH 0/7] replace rte atomics with GCC builtin atomics MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Date: Wed, 22 Mar 2023 15:58:07 +0100 Message-ID: <98CBD80474FA8B44BF855DF32C47DC35D877E6@smartserver.smartshare.dk> X-MimeOLE: Produced By Microsoft Exchange V6.5 In-Reply-To: <20230322142134.GA29057@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: [PATCH 0/7] replace rte atomics with GCC builtin atomics Thread-Index: AdlcyZ5rpcgBeZwWRGecPBOvSNPi/AAAVMoQ References: <1679084388-19267-1-git-send-email-roretzla@linux.microsoft.com> <20230317144226.2f26bad1@hermes.local> <20230317214910.GA31884@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> <98CBD80474FA8B44BF855DF32C47DC35D877E1@smartserver.smartshare.dk> <20230322142134.GA29057@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> From: =?iso-8859-1?Q?Morten_Br=F8rup?= To: "Tyler Retzlaff" Cc: "Stephen Hemminger" , , , , X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org > From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com] > Sent: Wednesday, 22 March 2023 15.22 >=20 > On Wed, Mar 22, 2023 at 12:28:44PM +0100, Morten Br=F8rup wrote: > > > From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com] > > > Sent: Friday, 17 March 2023 22.49 > > > > > > On Fri, Mar 17, 2023 at 02:42:26PM -0700, Stephen Hemminger wrote: > > > > On Fri, 17 Mar 2023 13:19:41 -0700 > > > > Tyler Retzlaff wrote: > > > > > > > > > Replace the use of rte_atomic.h types and functions, instead = use GCC > > > > > supplied C++11 memory model builtins. > > > > > > > > > > This series covers the libraries and drivers that are built on > Windows. > > > > > > > > > > The code has be converted to use the __atomic builtins but = there are > > > > > additional during conversion i notice that there may be some = issues > > > > > that need to be addressed. > > > > > > > > I don't think all these cmpset need to use SEQ_CST. > > > > Especially for the places where it is used a loop, might > > > > be more efficient with some of the other memory models. > > > > > > i agree. > > > > > > however, i'm not trying to improve the code with this change, just > > > decouple it from rte_atomics.h so trying my best to avoid any > > > unnecessary semantic change. > > > > > > certainly if the maintainers of this code wish to weaken the = ordering > > > where appropriate after the change is merged they can do so and = handily > > > this change has enabled them to do so easily allowing them to test = just > > > their change in isolation. > > > > I agree with the two-step approach, where this first step is a = simple > search-and-replacement; but I insist that you add a FIXME or similar = note > where you have blindly used SEQ_CST, indicating that the memory order = needs to > be reviewed and potentially corrected. >=20 > i think the maintainers need to take some responsibility, if they see > optimizations they missed when previously writing the code they need = to > follow up with a patch themselves. i can't do everything for them and > marking things i'm not sure about will only lead to me having to churn > patch series to remove the unwanted comments later. The previous atomic functions didn't have the "memory order" parameter, = so the maintainers didn't have to think about it - and thus they didn't = miss any optimizations when accepting the code. I also agree 100 % that it is not your responsibility to consider or = determine which memory order is appropriate! But I think you should mark the locations where you are changing from = the old rte_atomic functions (where no memory order optimization was = available) to the new functions - to highlight where the option of = memory ordering has been introduced and knowingly ignored (by you). >=20 > keep in mind i have to touch each of these again when converting to > standard so that's a better time to review ~everything in more detail > because when converting to standard that's when suddenly you get a = bunch > of code generation that is "fallback" to seq_cst that isn't happening = now. I think you should to do it when replacing the rte_atomic functions with = the __atomic functions. It will make it easier to see where the memory = order was knowingly ignored, and should be reviewed for optimization. >=20 > the series that converts to standard needs to be up for review as soon > as possible to maximize available time for feedback before 23.11 so it > would be better to get the simpler cut & paste normalizing the code = out > of the way to unblock that series submission. >=20 > > > > Also, in a couple of the drivers, you are using int64_t for packet = counters. > These cannot be negative and should be uint64_t. And AFAIK, such = counters can > use RELAXED memory order. >=20 > i know you don't mean to say i selected the types and rather that the > types that were selected are not quite correct for their usage. Yes; the previous types were also signed, and you didn't change that. > again > on the review that actually adopts std atomics is a better place to = make > any potential type changes since we are "breaking" the API for 23.11 > anyway. further, the std atomics series technically changes all the > types so it's probably better to make one type change then rather than > one now and one later. >=20 > i think it would be best to get these validated and merged asap so we > can get to the std atomics review. when that series is up let's = discuss > further how i can mark areas of concern, with that series i expect = there > will have to be some changes in order to avoid minor regressions. >=20 > thanks! I thought it would be better to catch these details (i.e. memory = ordering and signedness) early on, but I now understand that you planned = to do it in a later step. So I'll let you proceed as you have planned. Thanks for all your work on this, Tyler. It is much appreciated! -Morten