> > -----Original Message----- > > From: dev <dev-boun...@dpdk.org> On Behalf Of Stephen Hemminger > > Sent: Monday, February 24, 2020 1:35 PM > > To: Jerin Jacob <jerinjac...@gmail.com> > > Cc: Konstantin Ananyev <konstantin.anan...@intel.com>; dpdk-dev > > <dev@dpdk.org>; Olivier Matz <olivier.m...@6wind.com> > > Subject: Re: [dpdk-dev] [RFC 0/6] New sync modes for ring > > > > On Mon, 24 Feb 2020 23:29:57 +0530 > > Jerin Jacob <jerinjac...@gmail.com> wrote: > > > > > On Mon, Feb 24, 2020 at 10:29 PM Stephen Hemminger > > > <step...@networkplumber.org> wrote: > > > > > > > > On Mon, 24 Feb 2020 11:35:09 +0000 > > > > Konstantin Ananyev <konstantin.anan...@intel.com> wrote: > > > > > > > > > Upfront note - that RFC is not a complete patch. > > > > > It introduces an ABI breakage, plus it doesn't update ring_elem > > > > > code properly, etc. > > > > > I plan to deal with all these things in later versions. > > > > > Right now I seek an initial feedback about proposed ideas. > > > > > Would also ask people to repeat performance tests (see below) on > > > > > their platforms to confirm the impact. > > > > > > > > > > More and more customers use(/try to use) DPDK based apps within > > > > > overcommitted systems (multiple acttive threads over same pysical > > cores): > > > > > VM, container deployments, etc. > > > > > One quite common problem they hit: Lock-Holder-Preemption with > > rte_ring. > > > > > LHP is quite a common problem for spin-based sync primitives > > > > > (spin-locks, etc.) on overcommitted systems. > > > > > The situation gets much worse when some sort of fair-locking > > > > > technique is used (ticket-lock, etc.). > > > > > As now not only lock-owner but also lock-waiters scheduling order > > > > > matters a lot. > > > > > This is a well-known problem for kernel within VMs: > > > > > http://www-archive.xenproject.org/files/xensummitboston08/LHP.pdf > > > > > https://www.cs.hs-rm.de/~kaiser/events/wamos2017/Slides/selcuk.pdf > > > > > The problem with rte_ring is that while head accusion is sort of > > > > > un-fair locking, waiting on tail is very similar to ticket lock > > > > > schema - tail has to be updated in particular order. > > > > > That makes current rte_ring implementation to perform really pure > > > > > on some overcommited scenarios. > > > > > > > > Rather than reform rte_ring to fit this scenario, it would make more > > > > sense to me to introduce another primitive. The current lockless > > > > ring performs very well for the isolated thread model that DPDK was > > > > built around. This looks like a case of customers violating the > > > > usage model of the DPDK and then being surprised at the fallout. > > > > > > I agree with Stephen here. > > > > > > I think, adding more runtime check in the enqueue() and dequeue() will > > > have a bad effect on the low-end cores too. > > > But I agree with the problem statement that in the virtualization use > > > case, It may be possible to have N virtual cores runs on a physical > > > core. > > > > > > IMO, The best solution would be keeping the ring API same and have a > > > different flavor in "compile-time". Something like liburcu did for > > > accommodating different flavors. > > > > > > i.e urcu-qsbr.h and urcu-bp.h will identical definition of API. The > > > application can simply include ONE header file in a C file based on > > > the flavor. > > > If need both at runtime. Need to have function pointer or so in the > > > application and define the function in different c file by including > > > the approaite flavor in C file. > > > > This would also be a good time to consider the tradeoffs of the heavy use of > > inlining that is done in rte_ring vs the impact that has on API/ABI > > stability. > > > I was working on few requirements in rte_ring library for RCU defer APIs. RFC > is at https://patchwork.dpdk.org/cover/66020/.
Yep, noticed your patch, seems we sort of collided here. As I understand you patch aims to provide functionality similar to my HTS one. Will try to look at yours one in next fee days, hopefully we can end-up with some common denominator. Konstantin
