Re: [dpdk-dev] [RFC PATCH 3/3] lib/lpm: integrate RCU QSBR

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 22 Aug 2019 14:34:57 +0800
Ruifeng Wang <ruifeng.wang@arm.com> wrote:

> Currently, the tbl8 group is freed even though the readers might be
> using the tbl8 group entries. The freed tbl8 group can be reallocated
> quickly. This results in incorrect lookup results.
> 
> RCU QSBR process is integrated for safe tbl8 group reclaim.
> Refer to RCU documentation to understand various aspects of
> integrating RCU library into other libraries.
> 
> Signed-off-by: Ruifeng Wang <ruifeng.wang@arm.com>
> Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> Reviewed-by: Gavin Hu <gavin.hu@arm.com>

Having RCU in LPM is a good idea but difficult to find out how to
do it in DPDK. Not everyone wants to use RCU, so making a required part
of how LPM is used will impact users.

Also, it looks like DPDK RCU lacks a good generic way to handle deferred
free. Having to introduce a ring to handle is adding more complexity when
a generic solution would be better (see userspace RCU library for example).
Other parts of DPDK would benefit if deferred free was done better.