Bill Fischofer(Bill-Fischofer-Linaro) replied on github web page:
platform/linux-generic/include/odp_buffer_internal.h
line 17
@@ -41,11 +41,19 @@ typedef struct seg_entry_t {
uint32_t len;
} seg_entry_t;
+typedef union buffer_index_t {
+ uint32_t u32;
+
+ struct {
+ uint32_t pool :8;
+ uint32_t buffer :24;
Comment:
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_r169819392
updated_at 2018-02-22 09:32:40
