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

[Suanming Mou <suanmingm@mellanox.com>]

Hi 

> -----Original Message-----
> From: Dumitrescu, Cristian <cristian.dumitrescu@intel.com>
> Sent: Wednesday, April 8, 2020 1:48 AM
> To: Suanming Mou <suanmingm@mellanox.com>
> Cc: dev@dpdk.org
> Subject: RE: [PATCH 1/2] bitmap: add create bitmap with all bits set
> 
> 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 for the suggestion. Will update.
> 
> Thanks,
> Cristian