Re: [dpdk-dev] [PATCH 1/2] bitmap: add create bitmap with all bits set

["Dumitrescu, Cristian" <cristian.dumitrescu@intel.com>]

Hi Suanming,

> -----Original Message-----
> From: Suanming Mou <suanmingm@mellanox.com>
> Sent: Tuesday, March 10, 2020 8:21 AM
> To: Dumitrescu, Cristian <cristian.dumitrescu@intel.com>
> Cc: dev@dpdk.org
> Subject: [PATCH 1/2] bitmap: add create bitmap with all bits set
> 
> Currently, in the case to use bitmap as resource allocator, after
> bitmap creation, all the bitmap bits should be set to indicate the
> bit available. Every time when allocate one bit, search for the set
> bits and clear it to make it in use.
> 
> Add a new rte_bitmap_init_with_all_set() function to have a quick
> fill up the bitmap bits.
> 
> Comparing with the case create the bitmap as empty and set the bitmap
> one by one, the new function costs less cycles.
> 
> Signed-off-by: Suanming Mou <suanmingm@mellanox.com>
> ---
>  lib/librte_eal/common/include/rte_bitmap.h | 32
> ++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/lib/librte_eal/common/include/rte_bitmap.h
> b/lib/librte_eal/common/include/rte_bitmap.h
> index 6b846f2..36b32e4 100644
> --- a/lib/librte_eal/common/include/rte_bitmap.h
> +++ b/lib/librte_eal/common/include/rte_bitmap.h
> @@ -483,6 +483,38 @@ struct rte_bitmap {
>  	return 0;
>  }
> 
> +/**
> + * Bitmap initialization with all bits set
> + *
> + * @param n_bits
> + *   Number of pre-allocated bits in array2.
> + * @param mem
> + *   Base address of array1 and array2.
> + * @param mem_size
> + *   Minimum expected size of bitmap.
> + * @return
> + *   Handle to bitmap instance.
> + */
> +static inline struct rte_bitmap *
> +rte_bitmap_init_with_all_set(uint32_t n_bits, uint8_t *mem, uint32_t
> mem_size)
> +{
> +	uint32_t i;
> +	uint32_t slabs = n_bits / RTE_BITMAP_SLAB_BIT_SIZE;
> +	struct rte_bitmap *bmp = rte_bitmap_init(n_bits, mem, mem_size);
> +
> +	if (!bmp)
> +		return NULL;
> +	/* Fill the arry2 byte aligned bits. */
> +	memset(bmp->array2, 0xff, slabs * sizeof(bmp->array2[0]));
> +	/* Fill the arry1 bits. */
> +	for (i = 0; i < n_bits; i += RTE_BITMAP_CL_BIT_SIZE)
> +		rte_bitmap_set(bmp, i);
> +	/* Fill the arry2 left not byte aligned bits. */
> +	for (i = slabs * RTE_BITMAP_SLAB_BIT_SIZE; i < n_bits; i++)
> +		rte_bitmap_set(bmp, i);
> +	return bmp;
> +}
> +
>  #ifdef __cplusplus
>  }
>  #endif
> --
> 1.8.3.1

I agree that starting with all bits set could be very useful for some apps.

I agree that having a customized implementation for starting with all bits set -- as opposed to simply start with all bits cleared and calling the API in a loop to set each bit -- could be useful, as it could reduce the initialization time.

What I don't understand is your implementation of it: why still calling the API to set all bits in a loop? If we are to add this, I suggest we create a fully customized implementation that sets the fields on struct rte_bitmap to the right values. Makes sense?

Thanks,
Cristian