RE: [PATCH bpf-next 2/2] net: xdp: add xdp_update_skb_shared_info utility routine
From: John Fastabend <john.fastabend@gmail.com>
Date: 2021-07-12 18:46:31
Also in:
bpf
Lorenzo Bianconi wrote:
Introduce xdp_update_skb_shared_info routine to update frags array metadata from a given xdp_buffer/xdp_frame. We do not need to reset frags array since it is already initialized by the driver. Rely on xdp_update_skb_shared_info in mvneta driver.
Some more context here would really help. I had to jump into the mvneta
driver to see what is happening.
So as I read this we have a loop processing the descriptor in
mvneta_rx_swbm()
mvneta_rx_swbm()
while (rx_proc < budget && rx_proc < rx_todo) {
if (rx_status & MVNETA_RXD_FIRST_DESC) ...
else {
mvneta_swbm_add_rx_fragment()
}
..
if (!rx_status & MVNETA_RXD_LAST_DESC)
continue;
..
if (xdp_prog)
mvneta_run_xdp(...)
}
roughly looking like above. First question, do you ever hit
!MVNETA_RXD_LAST_DESC today? I assume this is avoided by hardware
setup when XDP is enabled, otherwise _run_xdp() would be
broken correct? Next question, given last descriptor bit
logic whats the condition to hit the code added in this patch?
wouldn't we need more than 1 descriptor and then we would
skip the xdp_run... sorry lost me and its probably easier
to let you give the flow vs spending an hour trying to
track it down.
But, in theory as you handle a hardware discriptor you can build
up a set of pages using them to create a single skb rather than a
skb per descriptor. But don't we know if pfmemalloc should be
done while we are building the frag list? Can't se just set it
vs this for loop in xdp_update_skb_shared_info(),
+ for (i = 0; i < nr_frags; i++) {
+ struct page *page = skb_frag_page(&sinfo->frags[i]);
+
+ page = compound_head(page);
+ if (page_is_pfmemalloc(page)) {
+ skb->pfmemalloc = true;
+ break;
+ }
+ }
+}...
quoted hunk ↗ jump to hunk
diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c index 361bc4fbe20b..abf2e50880e0 100644 --- a/drivers/net/ethernet/marvell/mvneta.c +++ b/drivers/net/ethernet/marvell/mvneta.c@@ -2294,18 +2294,29 @@ mvneta_swbm_add_rx_fragment(struct mvneta_port *pp, rx_desc->buf_phys_addr = 0; if (data_len > 0 && xdp_sinfo->nr_frags < MAX_SKB_FRAGS) { - skb_frag_t *frag = &xdp_sinfo->frags[xdp_sinfo->nr_frags++]; + skb_frag_t *frag = &xdp_sinfo->frags[xdp_sinfo->nr_frags]; skb_frag_off_set(frag, pp->rx_offset_correction); skb_frag_size_set(frag, data_len); __skb_frag_set_page(frag, page); + /* We don't need to reset pp_recycle here. It's already set, so + * just mark fragments for recycling. + */ + page_pool_store_mem_info(page, rxq->page_pool); + + /* first fragment */ + if (!xdp_sinfo->nr_frags) + xdp_sinfo->gso_type = *size;
Would be nice to also change 'int size' -> 'unsigned int size' so the types matched. Presumably you really can't have a negative size. Also how about giving gso_type a better name. xdp_sinfo->size maybe?
+ xdp_sinfo->nr_frags++;
/* last fragment */
if (len == *size) {
struct skb_shared_info *sinfo;
sinfo = xdp_get_shared_info_from_buff(xdp);
+ sinfo->xdp_frags_tsize = xdp_sinfo->nr_frags * PAGE_SIZE;
sinfo->nr_frags = xdp_sinfo->nr_frags;
+ sinfo->gso_type = xdp_sinfo->gso_type;
memcpy(sinfo->frags, xdp_sinfo->frags,
sinfo->nr_frags * sizeof(skb_frag_t));
}Thanks, John