> On Tue, Jul 6, 2021 at 4:53 AM Lorenzo Bianconi > <lorenzo.bianconi@xxxxxxxxxx> wrote: > > > > > On Mon, Jul 5, 2021 at 8:52 AM Lorenzo Bianconi > > > <lorenzo.bianconi@xxxxxxxxxx> wrote: > > > > > > > > > On Tue, Jun 29, 2021 at 5:43 AM Lorenzo Bianconi > > > > > <lorenzo.bianconi@xxxxxxxxxx> wrote: > > > > [...] > > > > > > Hi Lorenzo, > > > > > > What about doing something like breaking up the type value in > > > xdp_mem_info? The fact is having it as an enum doesn't get us much > > > since we have a 32b type field but are only storing 4 possible values > > > there currently > > > > > > The way I see it, scatter-gather is just another memory model > > > attribute rather than being something entirely new. It makes as much > > > sense to have a bit there for MEM_TYPE_PAGE_SG as it does for > > > MEM_TYPE_PAGE_SHARED. I would consider either splitting the type field > > > into two 16b fields. For example you might have one field that > > > describes the source pool which is currently either allocated page > > > (ORDER0, SHARED), page_pool (PAGE_POOL), or XSK pool (XSK_BUFF_POOL), > > > and then two flags for type with there being either shared and/or > > > scatter-gather. > > > > Hi Alex, > > > > I am fine reducing the xdp_mem_info size defining type field as u16 instead of > > u32 but I think mb is a per-xdp_buff/xdp_frame property since at runtime we can > > receive a tiny single page xdp_buff/xdp_frame and a "jumbo" xdp_buff/xdp_frame > > composed by multiple pages. According to the documentation available in > > include/net/xdp.h, xdp_rxq_info (where xdp_mem_info is contained for xdp_buff) > > is "associated with the driver level RX-ring queues and it is information that > > is specific to how the driver have configured a given RX-ring queue" so I guess > > it is a little bit counterintuitive to add this info there. > > It isn't really all that counterintuitive. However it does put the > onus on the driver to be consistent about things. So even a > single-buffer xdp_buff would technically have to be a scatter-gather > buff, but it would have no fragments in it. So the requirement would > be to initialize the frags and data_len fields to 0 for all xdp_buff > structures. nr_frags and data_len are currently defined in skb_shared_info(xdp_buff) so I guess initialize them to 0 will trigger a cache miss (in fact we introduced the mb bit just to avoid this initialization and introduce penalties for legacy single-buffer use-case). Do you mean to have these fields in xdp_buff/xdp_frame structure? > > > Moreover we have the "issue" for devmap in dev_map_bpf_prog_run() when we > > perform XDP_REDIRECT with the approach you proposed and last we can reuse this > > new flags filed for XDP hw-hints support. > > What about reducing xdp_mem_info and add the flags field in xdp_buff/xdp_frame > > in order to avoid increasing the xdp_buff/xdp_frame size? Am I missing > > something? > > The problem is there isn't a mem_info field in the xdp_buff. It is in > the Rx queue info structure. yes, this is what I meant :) Regards, Lorenzo > > Thanks, > > - Alex >
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