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:[email protected]] >Sent: Tuesday, July 10, 2018 11:00 AM >To: Wang, Yipeng1 <[email protected]>; De Lara Guarch, Pablo ><[email protected]> >Cc: [email protected]; Richardson, Bruce <[email protected]>; >[email protected]; [email protected]; nd ><[email protected]> >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 <[email protected]> >Sent: Monday, July 9, 2018 5:45 AM >To: [email protected] >Cc: [email protected]; [email protected]; [email protected]; Honnappa >Nagarahalli <[email protected]>; >[email protected]; [email protected] >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. > >
