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
