> -----Original Message----- > From: Michael Baum <michae...@nvidia.com> > Sent: Tuesday, January 31, 2023 2:07 AM > To: Akhil Goyal <gak...@marvell.com>; dev@dpdk.org; Mahipal Challa > <mcha...@marvell.com>; Fan Zhang <fanzhang....@gmail.com>; Ashish Gupta > <ashi...@marvell.com> > Cc: Matan Azrad <ma...@nvidia.com>; Fiona Trahe <fiona.tr...@intel.com>; > NBU-Contact-Thomas Monjalon (EXTERNAL) <tho...@monjalon.net> > Subject: RE: [EXT] [PATCH 1/4] compressdev: add LZ4 algorithm support > > On Mon, Jan 30, 2023 at 20:35 PM Akhil Goyal <gak...@marvell.com> wrote: > > > > > +/** > > > + * Block checksum flag. > > > + * If this flag is set, each data block will be followed by a 4-bytes > > > checksum, > > > + * calculated by using the xxHash-32 algorithm on the raw (compressed) > data > > > + * block. The intention is to detect data corruption (storage or > > > transmission > > > + * errors) immediately, before decoding. Block checksum usage is > > > optional. > > > + */ > > > +#define RTE_COMP_LZ4_FLAG_BLOCK_CHECKSUM (1 << 4) > > > + > > > +/** > > > + * Block Independence flag. > > > + * If this flag is set to 1, blocks are independent. > > > + * If this flag is set to 0, each block depends on previous ones (up to > > > LZ4 > > > + * window size, which is 64 KB). In such case, it is necessary to decode > > > all > > > + * blocks in sequence. > > > + * Block dependency improves compression ratio, especially for small > blocks. > > > On > > > + * the other hand, it makes random access or multi-threaded decoding > > > impossible. > > > + */ > > > +#define RTE_COMP_LZ4_FLAG_BLOCK_INDEPENDENCE (1 << 5) > > > > Why did you start with 4th and 5th bit of the flags? Why not first two bits? > > I didn't choose the values by myself, I took them from LZ4 standard: > https://github.com/lz4/lz4/blob/dev/doc/lz4_Frame_format.md#frame-descriptor
Ok, Are we defining and making the frame descriptor inside library? Also, why all the bits not added? I believe these are just flags which PMD would use to make the frame descriptors. If so, we should start with 0th bit and let the PMD handle bit shifting.
