Re: [PATCH] mempool: introduce flag to indicate hw mempool

[Olivier Matz <olivier.matz@6wind.com>]

Hi Hemant,

On Mon, 3 Apr 2017 14:42:09 +0530, Hemant Agrawal <hemant.agrawal@nxp.com> wrote:
> Hardware pools need to distinguish between buffers allocated using
> software or hardware backed pools.
> 
> Some HW NICs may choose to autonomously free the pickets during
> transmit if the packet is from HW pool. While they should not do
> it for software backed pools.
> 
> Such flag would also help when multiple pools are being handled by
> a PMD, saving costly compare operations for any internal marker.
> 
> Signed-off-by: Hemant Agrawal <hemant.agrawal@nxp.com>
> ---
>  lib/librte_mempool/rte_mempool.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/lib/librte_mempool/rte_mempool.h b/lib/librte_mempool/rte_mempool.h
> index 991feaa..91dbd21 100644
> --- a/lib/librte_mempool/rte_mempool.h
> +++ b/lib/librte_mempool/rte_mempool.h
> @@ -263,6 +263,11 @@ struct rte_mempool {
>  #define MEMPOOL_F_SC_GET         0x0008 /**< Default get is "single-consumer".*/
>  #define MEMPOOL_F_POOL_CREATED   0x0010 /**< Internal: pool is created. */
>  #define MEMPOOL_F_NO_PHYS_CONTIG 0x0020 /**< Don't need physically contiguous objs. */
> +#define MEMPOOL_F_HW_POOL        (1 << ((sizeof(int) * 8) - 1)) /**< Internal:
> +	* Hardware offloaded pool. This information may be used by the
> +	* NIC or other hw. Some NICs autonomously free the HW backed pool packets. */
> +
> +/**< Don't need physically contiguous objs. */
>  
>  /**
>   * @internal When debug is enabled, store some statistics.


One thing is still not clear to me: in your driver, you check this flag:
- if it is unset, you reallocate a packet from your hw pool, you copy
  some metadata, and you send it to the hw.
- if it is set, you assume that you can call mempool_to_bpid(mp) and directly
  send it to the hw.

I think this is not correct. The test you want to do in your driver is:
"is it the pool that I registered for my hardware"?
It is not:
"is it a hardware managed pool?".

I think what you are doing here prevents to use 2 hardware mempools
at the same time, because they would all have this flag, and mempool_to_bpid()
would probably crash.

Instead, can't you just compare the mempool pointer to a value stored internally
in the driver?

Olivier