Re: [dpdk-dev] [PATCH v2 1/3] net/af_xdp: allow bigger batch sizes

["Loftus, Ciara" <ciara.loftus@intel.com>]

> 
> On 3/9/2021 10:19 AM, Ciara Loftus wrote:
> > Prior to this commit, the maximum batch sizes for zero-copy and copy-
> mode
> > rx and copy-mode tx were set to 32. Apart from zero-copy tx, the user
> > could never rx/tx any more than 32 packets at a time and without
> inspecting
> > the code the user wouldn't be aware of this.
> >
> > This commit removes these upper limits placed on the user and instead
> > sets an internal batch size equal to the default ring size (2048). Batches
> > larger than this are still processed, however they are split into smaller
> > batches similar to how it's done in other drivers. This is necessary
> > because some arrays used during rx/tx need to be sized at compile-time.
> >
> > Allowing a larger batch size allows for fewer batches and thus larger bulk
> > operations, fewer ring accesses and fewer syscalls which should yield
> > improved performance.
> >
> > Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
> > ---
> >   drivers/net/af_xdp/rte_eth_af_xdp.c | 67
> ++++++++++++++++++++++++-----
> >   1 file changed, 57 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/net/af_xdp/rte_eth_af_xdp.c
> b/drivers/net/af_xdp/rte_eth_af_xdp.c
> > index 3957227bf0..be524e4784 100644
> > --- a/drivers/net/af_xdp/rte_eth_af_xdp.c
> > +++ b/drivers/net/af_xdp/rte_eth_af_xdp.c
> > @@ -66,8 +66,8 @@ RTE_LOG_REGISTER(af_xdp_logtype,
> pmd.net.af_xdp, NOTICE);
> >   #define ETH_AF_XDP_DFLT_START_QUEUE_IDX	0
> >   #define ETH_AF_XDP_DFLT_QUEUE_COUNT	1
> >
> > -#define ETH_AF_XDP_RX_BATCH_SIZE	32
> > -#define ETH_AF_XDP_TX_BATCH_SIZE	32
> > +#define ETH_AF_XDP_RX_BATCH_SIZE
> 	XSK_RING_CONS__DEFAULT_NUM_DESCS
> > +#define ETH_AF_XDP_TX_BATCH_SIZE
> 	XSK_RING_CONS__DEFAULT_NUM_DESCS
> >
> 
> Just to double check, can there be a library version that these macros not
> defined, should it be checked?

There can't be a library version with AF_XDP support without these macros, as they've been around since the very beginning:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1cad078842396
We only build the PMD if xsk.h is available, and since these macros have been in the file since it has existed, we're safe.