Hi everyone,
> On Sun, Aug 20, 2023 at 11:07:33AM +0200, Morten Brørup wrote: > > Bruce, Honnappa, Konstantin, > > > > Back in 2017, Bruce added support for non-power-of-2 rings with this patch > > [1]. > > > > [1]: > > https://git.dpdk.org/dpdk/commit/lib/librte_ring/rte_ring.h?id=b74461155543430f5253e96ad6d413ebcad36693 > > > > I think that the calculation of "entries" in __rte_ring_move_cons_head() > > [2][3] is incorrect when the ring capacity is not power-of-2, > because it is missing the capacity comparison you added to rte_ring_count() > [4]. Please review if I'm mistaken. > > > > [2]: > > https://elixir.bootlin.com/dpdk/v23.07/source/lib/ring/rte_ring_c11_pvt.h#L159 > > [3]: > > https://elixir.bootlin.com/dpdk/v23.07/source/lib/ring/rte_ring_generic_pvt.h#L150 > > [4]: https://elixir.bootlin.com/dpdk/v23.07/source/lib/ring/rte_ring.h#L502 Just to confirm you suggest something like that: - *entries = (r->prod.tail - *old_head); + count = (r->prod.tail - *old_head); + entries = (count > r->capacity) ? r->capacity : count; right? > > > thanks for flagging this inconsistency, but I think we are ok. > > For consumer, I think this is correct, because we are only ever reducing > the number of entries in the ring, and the calculation of the number of > entries is made in the usual way using modulo arithmetic. We should never > have more than capacity entries in the ring so the check in ring count I > believe is superflous. [The exception would be if someone bypassed the > inline functions and accessed the ring directly themselves - at which point > "all bets are off", to use the English phrase] > > The producer code (__rte_ring_move_prod_head) does do a capacity check, > which is where one is required to ensure we never exceed capacity. I also can't come up with the case, when current code will cause an issue.. In properly operating ring, I think we should never have more then r->capacity entries populated, so this extra check can be skipped. Unless you do have some particular case in mind? Konstantin
