Petri Savolainen(psavol) replied on github web page: platform/linux-generic/include/odp_ring_st_internal.h line 46 @@ -0,0 +1,118 @@ +/* Copyright (c) 2018, Linaro Limited + * All rights reserved. + * + * SPDX-License-Identifier: BSD-3-Clause + */ + +#ifndef ODP_RING_ST_INTERNAL_H_ +#define ODP_RING_ST_INTERNAL_H_ + +#ifdef __cplusplus +extern "C" { +#endif + +#include <odp/api/hints.h> +#include <odp_align_internal.h> + +/* Basic ring for single thread usage. Operations must be synchronized by using + * locks (or other means), when multiple threads use the same ring. */ +typedef struct { + uint32_t head; + uint32_t tail; + uint32_t mask; + uint32_t *data; + +} ring_st_t; + +/* Initialize ring. Ring size must be a power of two. */ +static inline void ring_st_init(ring_st_t *ring, uint32_t *data, uint32_t size) +{ + ring->head = 0; + ring->tail = 0; + ring->mask = size - 1; + ring->data = data; +} + +/* Dequeue data from the ring head. Max_num is smaller than ring size.*/ +static inline uint32_t ring_st_deq_multi(ring_st_t *ring, uint32_t data[], + uint32_t max_num) +{ + uint32_t head, tail, mask, idx; + uint32_t num, i; + + head = ring->head; + tail = ring->tail; + mask = ring->mask; + num = tail - head;
Comment: There's no need for abs(). Since it's all uint32_t variables, wrap a round is handled already. An example in 8bits: 0xff - 0xfd = 0x02 0x00 - 0xfe = 0x02 0x01 - 0xff = 0x02 0x02 - 0x00 = 0x02 This passes both gcc and clang, and is used already in the other ring implementation see ring_deq_multi(). > Petri Savolainen(psavol) wrote: > I prefer style with blank line in the end of a typedef, since it's easier to > spot the type name (as it's not mixed into struct field names). Checkpatch > passes so this style should be OK. >> Bill Fischofer(Bill-Fischofer-Linaro) wrote: >> Does this mean that sizes larger than 32 have no added performance benefit? >>> Bill Fischofer(Bill-Fischofer-Linaro) wrote: >>> Must use `CONFIG_QUEUE_SIZE - 1` here, as noted earlier, if we're not going >>> to use the user-supplied queue size. >>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote: >>>> Given its name, this looks like an extraneous statement that should be >>>> deleted. Renaming this to something like `prefetch_dequeued_bufs()` would >>>> make the intent clearer here. >>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote: >>>>> `if (!ring_st_is_empty(&queue->s.ring_st))` seems more natural here. >>>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote: >>>>>> Change to `if (param->size >= CONFIG_QUEUE_SIZE)` to handle the >>>>>> effective queue capacity. The user-supplied `size` should then be set to >>>>>> `ROUNDUP_POWER2_U32(size) - 1` for the masking to work properly. >>>>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote: >>>>>>> Same comment here as for plain queues. >>>>>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote: >>>>>>>> As noted earlier, due to "losing" one entry to distinguish queue >>>>>>>> empty/full, this should be returned as `CONFIG_QUEUE_SIZE - 1`, and we >>>>>>>> also need to ensure that `CONFIG_QUEUE_SIZE` is itself a power of 2. >>>>>>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote: >>>>>>>>> Since you're initializing `index.pool` and `index.buffer` there's no >>>>>>>>> need to set `index.u32` here. >>>>>>>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote: >>>>>>>>>> We originally had this index partitioning based on >>>>>>>>>> `ODP_CONFIG_POOLS`. Do we want to return to that here? >>>>>>>>>> >>>>>>>>>> If not, we at least need an `ODP_STATIC_ASSERT()` to ensure that >>>>>>>>>> `ODP_CONFIG_POOLS < 256` or else bad things will happen here. >>>>>>>>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote: >>>>>>>>>>> This routine can be optimized to: >>>>>>>>>>> ``` >>>>>>>>>>> return ring->head == ring->tail; >>>>>>>>>>> ``` >>>>>>>>>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote: >>>>>>>>>>>> Your invariant is the queue is empty when `head == tail` therefore >>>>>>>>>>>> the queue is full when `abs(tail - head) == mask`, so the correct >>>>>>>>>>>> calculation here is: >>>>>>>>>>>> >>>>>>>>>>>> `num = mask - abs(tail - head);` >>>>>>>>>>>> >>>>>>>>>>>> The effect is that a queue can only hold `size - 1` elements, >>>>>>>>>>>> otherwise you cannot distinguish between a full and an empty queue >>>>>>>>>>>> without another bit of metadata, which is a cost you're trying to >>>>>>>>>>>> avoid. >>>>>>>>>>>> >>>>>>>>>>>> This is somewhat problematic if the caller is trying to be >>>>>>>>>>>> "optimal" by specifying a power of two in the `size` parameter of >>>>>>>>>>>> the `odp_queue_param_t` passed to `odp_queue_create()`. For this >>>>>>>>>>>> reason we may wish to return a `max_size` of a power of 2 - 1 in >>>>>>>>>>>> `odp_queue_capability()` as part of this patch series. >>>>>>>>>>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote: >>>>>>>>>>>>> This only works if `size` is a power of 2. Should be documented >>>>>>>>>>>>> as such, since this is an internal routine. In this case an >>>>>>>>>>>>> `ODP_ASSERT(size == ROUNDUP_POWER2_U32(size))` for this >>>>>>>>>>>>> requirement would be a useful debugging aid. >>>>>>>>>>>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote: >>>>>>>>>>>>>> should be `num = abs(tail - head);` to deal with wrap arounds, >>>>>>>>>>>>>> otherwise may be misinterpreted as overly large since it's >>>>>>>>>>>>>> `uint32_t`. Note that GCC and clang recognize `abs()` and treat >>>>>>>>>>>>>> it as a builtin, so there's no actual `stdlib.h` call here. >>>>>>>>>>>>>>> Bill Fischofer(Bill-Fischofer-Linaro) wrote: >>>>>>>>>>>>>>> Extra blank line should be removed (nit). https://github.com/Linaro/odp/pull/492#discussion_r169872821 updated_at 2018-02-22 09:32:40