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Sat, 18 Nov 2023 03:04:46 -0500 (EST) From: Thomas Monjalon To: Bruce Richardson , =?utf-8?B?U3RhbmlzxYJhdw==?= Kardach , Tyler Retzlaff , Morten =?ISO-8859-1?Q?Br=F8rup?= Cc: dev@dpdk.org, Michal Mazurek , stable@dpdk.org Subject: Re: [PATCH] eal: fix alignment of RISCV xmm vector type Date: Sat, 18 Nov 2023 09:04:42 +0100 Message-ID: <1967357.usQuhbGJ8B@thomas> In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35E9F03A@smartserver.smartshare.dk> References: <1700083003-6641-1-git-send-email-roretzla@linux.microsoft.com> <98CBD80474FA8B44BF855DF32C47DC35E9F03A@smartserver.smartshare.dk> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="UTF-8" X-BeenThere: stable@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: patches for DPDK stable branches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: stable-bounces@dpdk.org 17/11/2023 12:18, Morten Br=C3=B8rup: > +CC Thomas, this patch is ready to be applied to 23.11. >=20 > > From: Bruce Richardson [mailto:bruce.richardson@intel.com] > > Sent: Friday, 17 November 2023 11.55 > >=20 > > On Thu, Nov 16, 2023 at 08:45:35AM +0100, Morten Br=C3=B8rup wrote: > > > > From: Stanis=C5=82aw Kardach [mailto:kda@semihalf.com] > > > > Sent: Thursday, 16 November 2023 00.21 > > > > > > > > On Wed, Nov 15, 2023 at 10:31=E2=80=AFPM Morten Br=C3=B8rup > > > > wrote: > > > > > > > > > > > From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com] > > > > > > Sent: Wednesday, 15 November 2023 22.17 > > > > > > > > > > > > Fix the alignment for rte_xmm_t it should be 16 instead of 8 > > bytes. > > > > > > > > > > > > Fixes: f22e705ebf12 ("eal/riscv: support RISC-V architecture") > > > > > > Cc: maz@semihalf.com > > > > > > Cc: stable@dpdk.org > > > > > > Signed-off-by: Tyler Retzlaff > > > > > > --- > > > > > > > > > > Reviewed-by: Morten Br=C3=B8rup > > > > > > > > > > As mentioned in the other thread: > > > > > > > > > > We need to urgently decide if this bug should live on in DPDK > > 23.11, > > > > or if the fix should be included although we are very late in the > > > > release process. > > > > > > > > > > Stanislaw, what do you think? > > > > Good catch! As for backporting I'm not sure of the urgency given > > that > > > > our examples still use scalar instructions for handling xmm_t. The > > > > question is whether there is a platform in use which has vector > > > > extensions enabled and that utilizes DPDK. I'm not that sure of it > > > > though I'd be happy to be proven wrong. > > > > > > Can we extrapolate this, and also conclude that postponing this > > bugfix until the next ABI/API breaking release, DPDK 24.11, is not > > really going to hurt anyone? > > > > > > Stanislaw, please confirm? > > > > > > Bruce, I don't feel 100 % confident in making this postponement > > recommendation. Could you please provide a second opinion regarding the > > timing of fixing this bug? Or rather: do you have any strong arguments > > *against* postponing it to DPDK 24.11? > > > > >=20 > > Not sure I'm any better placed to make an argument either way! >=20 > Bruce, I picked you because of your experience with vector code. >=20 > > However, I > > would very much tend to say that we should include this in 23.11, on > > the > > basis that if it turns out to be important we can't backport it later > > without affecting ABI. Right now, the code looks broken to me, and I'm > > also > > struggling to find circumstances where increasing the alignment will > > actually stop something from working. There could well be performance > > implications of having extra padding, but things should still work, > > AFAIK. > > On the other hand, if we don't include the fix, it is possible that a > > system (possibly a future one) could break and segfault due to > > incorrect > > vector code. I'd take a possible slowdown over a segfault! >=20 > The risk of slowdown isn't a factor for me at this stage. >=20 > I'm trying to balance the risk of fixing the bug vs. breaking something t= his late in the 23.11 release cycle. >=20 > You have a strong point that we also need to consider the bugfix in the c= ontext of the total lifetime of DPDK 23.11 in the wild. > With RISC-V's current traction, that certainly speaks in favor of includi= ng it in 23.11. >=20 > >=20 > > Is my assessment correct, or perhaps I'm missing some detail. >=20 > Thank you for your valuable feedback, Bruce. >=20 > I was just being overly cautious... After all, 23.11 is still at a stage = where bug fixes are accepted! >=20 > New conclusion: Let's get it into 23.11. Applied, thanks. I've kept CC:stable as it is a real fix. I don't see a problem in breaking API/ABI for RISC-V which is quite new. Anyway stable maintainers will choose what to do.