On 2021/2/8 16:40, Olivier Matz wrote: > Hi, > > On Mon, Feb 08, 2021 at 09:07:39AM +0100, Thomas Monjalon wrote: >> 08/02/2021 07:29, Chengchang Tang: >>> Hi, Thomas Monjalon and Ferruh Yigit and others. >>> >>> Here are two questions: >>> 1. What functions should be included in the 'tx_prepare' for PMDs? >>> 2. Whether an app must invoke 'rte_eth_tx_prepare' or under which >>> conditions an app must invoke the 'rte_eth_tx_prepare'? >> >> I would say by default the app should prepare the checksums, >> except if there is an explicit offload request (DEV_TX_OFFLOAD_*). >> I think the tx_prepare should only prepare the HW Tx offload >> if the offload is not entirely done in HW. > > On our side, we call tx_prepare() on a tx bulk if: > > 1/ a Tx offload is enabled on the port (DEV_TX_OFFLOAD_*) > 2/ at least one mbuf in the bulk has an offload flag among > PKT_TX_OFFLOAD_MASK > > The purpose of tx_prepare() is to check that offload can be done in hw, > and to prepare the packet data for the hw. For instance, niantics NICs > require that the L4 checksum in the packet is set to the pseudo-header > checksum. > > This could have be done in the tx() function, but it is a separated > function for 2 reasons: > - the application does not need to call it if it does not do hw tx offload > - the tx_prepare() function may modify packet data, which should not be the > case for tx(). In a pipeline model, these 2 functions may be called on > different cores. > > In my opinion, the tx_prepare() function should deal with outer checksums > preparation as well. > > Olivier > > .
Thank you, Thomas and Olivier. It's really helpful. Chengchang
