On 04/06/2015 03:31 PM, Bill Fischofer wrote:
> The /expression/ may be linear, but that doesn't imply that is how any
> given implementation needs to realize the expression. Since PMRs are
> reasonably static, I'd expect them to be "compiled" into whatever native
> classification capabilities are present in the platform. Real
> classification is typically done in parallel by the HW as the packet is
> coming "off the wire". This is necessary because one of the outputs of
> classification is pool selection, so all of this happens while the
> packet is in the HW's receive FIFO before the DMA engines are told where
> to store it.
Following our discussion on a call.
Choosing a pool on ingress solves two separate issues:
1. Isolation - packets that belong to different CoS'es may need to use
separate packet pools. Pool choice is strictly deterministic.
This case is covered by current API.
2. Segmentation optimization - application may want to sort packets of
different size into pools with different segment size. In this case
pool choice is not very strict. For example a small packet can be
allocated from a pool with big segments if small-segment pool is
empty. This case can't be expressed with a current API.
Assigning several pools to CoS and allowing implementation to pick an
optimal pool would be one option to solve #2.
During a meeting Maxim proposed to use a 'composite' pool instead, and
I like this idea more. I imagine something like this:
/**
* Create a composite pool
*
* This routine is used to create a pool which logically consists of
* a set of sub-pools. Each sub-pool has its own configuration
* parameters. Only pool of ODP_POOL_PACKET type can be created.
* On allocation an implementation will choose an optimal sub-pool to
* allocate a packet from.
* A composite pool can be used to optimize memory usage and minimize
* packet segmentation.
*
* @param name Name of the pool, max ODP_POOL_NAME_LEN-1 chars.
* May be specified as NULL for anonymous pools.
*
* @param shm The shared memory object in which to create the pool.
* Use ODP_SHM_NULL to reserve default memory type
* for the pool type.
*
* @param num_pools Number of sub-pools in a composite pool
*
* @param params Array of sub-pools' parameters.
*
* @return Handle of the created pool
* @retval ODP_POOL_INVALID Pool could not be created
*/
odp_pool_t odp_pool_create_composite(const char *name,
odp_shm_t shm,
uint32_t num_pools,
odp_pool_param_t *params[]);
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