From: Stephen Hemminger <email@example.com> To: Aaron Conole <firstname.lastname@example.org> Cc: David Marchand <email@example.com>, "Song\, Keesang" <Keesang.Song@amd.com>, "ktraynor\@redhat.com" <firstname.lastname@example.org>, "bluca\@debian.org" <email@example.com>, Thomas Monjalon <firstname.lastname@example.org>, "dev\@dpdk.org" <email@example.com>, "ferruh.yigit\@intel.com" <firstname.lastname@example.org>, "bruce.richardson\@intel.com" <email@example.com>, "honnappa.nagarahalli\@arm.com" <firstname.lastname@example.org>, "drc\@linux.vnet.ibm.com" <email@example.com>, "stable\@dpdk.org" <firstname.lastname@example.org>, "Grimm\, Jon" <Jon.Grimm@amd.com>, "Hollingsworth\, Brent" <email@example.com> Subject: Re: [dpdk-stable] [dpdk-dev] [PATCH 0/4] Extend --lcores to run on cores > RTE_MAX_LCORE Date: Fri, 21 Feb 2020 08:38:28 -0800 Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <email@example.com> On Fri, 21 Feb 2020 09:48:58 -0500 Aaron Conole <firstname.lastname@example.org> wrote: > David Marchand <email@example.com> writes: > > > On Fri, Feb 21, 2020 at 9:19 AM Song, Keesang <Keesang.Song@amd.com> wrote: > >> > >> [AMD Official Use Only - Internal Distribution Only] > > > > Please, get this header removed. > > This is a public mailing list. > > > > > >> Thanks Thomas for bringing this up. > >> I consider this is not a new feature, but rather a fix to address > >> the issue with statically assigned maximum lcore limit on > >> high-density CPU platform such as AMD Epyc. > >> As I see a lot of DPDK adopters are still using LTS 18.11 & 19.11, > >> and they have 1~2 yrs of lifetime left, we like to backport this to > >> LTS 18.11 & 19.11 at least. > > > > It is not a fix. > > > > The use of static arrays is a design choice that goes back to the > > early days in dpdk. > > The addition of --lcores came in after this, but it was introduced for > > a different use case than placing lcores on any physical core. > > And there was no claim that a core > RTE_MAX_LCORE would be usable. > > > > > > When testing on a new hardware, it is normal to observe some limitations. > > Running DPDK on those platforms should be possible: "should be" > > because I do not have access to this hardware and saw neither tests > > reports nor performance numbers. > > Before this patch, the limitation is that on Epyc, cores > > > RTE_MAX_LCORE are not usable. > > > > > > Now, this change is quite constrained. > > If we backport it, I don't expect issues in the main dpdk components > > (based on code review and ovs tests with a RTE_MAX_LCORE set to 16 on > > a 24 cores system). > > There might be issues in some examples or not widely used library > > which uses a physical core id instead of a lcore id. > > > > > > This is the same recurring question "do we allow new features in a > > stable branch?". > > Usually, the answer is 'no'. But we do allow some "new" things to be > backported (pci ids, etc) that might be required to enable older > functionality. Additionally, I'm sure if some feature were required to > mitigate a CVE, we'd rather favor backporting it. > > I guess we could pose a litmus test: > > 1. Is the problem this feature solves so widespread that it needs to > be addressed ASAP? > 2. Is there a known workaround to the problem this is solving? > 3. How intrusive is the feature? > 4. Is it shown to be stable in the mainline (number of fixes, testing, > etc)? > 5. Is it constrained enough that we know we can support it with even > higher priority than other things? > > Probably other questions that will need to be asked. > > And even in that list of question, I'm not sure I'd be able to advocate > backporting this in the upstream branches - it hasn't had much testing. > It's unstable. It's "difficult" to use. It is not widespread that > people have so many cores. The workaround is much simpler than > supporting this (recompile). > > > > > -- > > David Marchand > RTE_MAX_LCORES is exposed in API/ABI to application. Many applications use that to size internal data structures. Having rte_lcore_id() potentially return a larger value would cause out of bounds access (and crash) in that application.
next prev parent reply index Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <firstname.lastname@example.org> 2019-12-02 15:41 ` [dpdk-stable] [PATCH 1/4] eal/windows: fix cpuset macro name David Marchand [not found] ` <2076701.vBoWY3egPC@xps> 2020-02-21 8:04 ` [dpdk-stable] [dpdk-dev] [PATCH 0/4] Extend --lcores to run on cores > RTE_MAX_LCORE Thomas Monjalon 2020-02-21 8:19 ` Song, Keesang 2020-02-21 9:40 ` David Marchand 2020-02-21 14:48 ` Aaron Conole 2020-02-21 16:38 ` Stephen Hemminger [this message] 2020-05-29 3:05 ` Song, Keesang 2020-05-29 3:05 ` Song, Keesang 2020-06-01 21:22 ` Thomas Monjalon 2020-06-01 22:54 ` Song, Keesang 2020-06-09 16:30 ` Song, Keesang 2020-06-09 17:48 ` Luca Boccassi 2020-06-09 21:34 ` Kevin Traynor
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