Hi, Honnappa, Thanks for the comment.
RCU can handle one of the currency issue (key deletion while lookup) that has been discussed before, but we think it is not easy for RCU-alone to protect reader from cuckoo path displacement. Also, RCU solution requires user interaction. We agree that the current rwlock does not support preemptable writer. But a more advanced rwlock with priority could be implemented in the future into the rwlock library. Thanks Yipeng >-----Original Message----- >From: Honnappa Nagarahalli [mailto:honnappa.nagaraha...@arm.com] >Sent: Tuesday, July 10, 2018 11:00 AM >To: Wang, Yipeng1 <yipeng1.w...@intel.com>; De Lara Guarch, Pablo ><pablo.de.lara.gua...@intel.com> >Cc: dev@dpdk.org; Richardson, Bruce <bruce.richard...@intel.com>; >vgu...@caviumnetworks.com; brijesh.s.si...@gmail.com; nd ><n...@arm.com> >Subject: RE: [PATCH v4 0/8] Add read-write concurrency to rte_hash library > >Hi Yipeng/Pablo, > Apologies for my delayed comments > >-----Original Message----- >From: Yipeng Wang <yipeng1.w...@intel.com> >Sent: Monday, July 9, 2018 5:45 AM >To: pablo.de.lara.gua...@intel.com >Cc: dev@dpdk.org; yipeng1.w...@intel.com; bruce.richard...@intel.com; Honnappa >Nagarahalli <honnappa.nagaraha...@arm.com>; >vgu...@caviumnetworks.com; brijesh.s.si...@gmail.com >Subject: [PATCH v4 0/8] Add read-write concurrency to rte_hash library > >This patch set adds the read-write concurrency support in rte_hash. >A new flag value is added to indicate if read-write concurrency is needed >during creation time. Test cases are implemented to do >functional and performance tests. > >The new concurrency model is based on rte_rwlock. When Intel TSX is available >and the users indicate to use it, the TM version of the >rte_rwlock will be called. Both multi-writer and read-write concurrency are >protected by the rte_rwlock instead of the x86 specific >RTM instructions, so the x86 specific header rte_cuckoo_hash_x86.h is removed >and the code is infused into the main .c file. > >IMO, at a high-level, there are two use cases for the rte_hash library: >1) Writers are on control plane and data plane are readers >2) Writers and readers are on data plane > >This distinction is required as in the case of 1) writers are pre-emptible. If >I consider platforms without TSX (I do not know how Intel >TSX works), the rte_rwlock implementation is blocking. A writer on the control >plane can take the lock and get pre-empted. Since >rte_rwlock is used for read-write concurrency, it will block the readers (on >the data plane) for an extended duration. I think, support >for RCU is required to solve this issue. > >
