Because otherwise when crc computation is still needed it's way more
expensive than on a linear buffer to the point that it affects
performance.
It's so expensive that netperf test gives a perf output as below:
Overhead Shared Object Symbol
69,44% [kernel] [k] gf2_matrix_square
2,84% [kernel] [k] crc32_generic_combine.part.0
2,78% [kernel] [k] _raw_spin_lock_bh
And performance goes from 2Gbit/s to 0.5Gbit/s on this test. Doing the
linearization before checksumming is enough to restore it.
Fixes: 3acb50c18d8d ("sctp: delay as much as possible skb_linearize")
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
---
Please consider this to -stable too as v4.7 performance is affected.
Thanks
net/sctp/input.c | 11 +++++++----
net/sctp/inqueue.c | 13 -------------
2 files changed, 7 insertions(+), 17 deletions(-)
diff --git a/net/sctp/input.c b/net/sctp/input.c
index c182db7d691ff44a52923fb36c9170e49c141c04..69444d32ecda6cd1a4924911172feba89c5ae976 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -119,7 +119,13 @@ int sctp_rcv(struct sk_buff *skb)
skb_transport_offset(skb))
goto discard_it;
- if (!pskb_may_pull(skb, sizeof(struct sctphdr)))
+ /* If the packet is fragmented and we need to do crc checking,
+ * it's better to just linearize it otherwise crc computing
+ * takes longer.
+ */
+ if ((!(skb_shinfo(skb)->gso_type & SKB_GSO_SCTP) &&
+ skb_linearize(skb)) ||
+ !pskb_may_pull(skb, sizeof(struct sctphdr)))
goto discard_it;
/* Pull up the IP header. */
@@ -1177,9 +1183,6 @@ static struct sctp_association *__sctp_rcv_lookup_harder(struct net *net,
if ((skb_shinfo(skb)->gso_type & SKB_GSO_SCTP) == SKB_GSO_SCTP)
return NULL;
- if (skb_linearize(skb))
- return NULL;
-
ch = (sctp_chunkhdr_t *) skb->data;
/* The code below will attempt to walk the chunk and extract
diff --git a/net/sctp/inqueue.c b/net/sctp/inqueue.c
index c30ddb0f31907f57c5ce85b00dbe04260ca1cb2e..6437aa97cfd79f14c633499c2b131389204c435b 100644
--- a/net/sctp/inqueue.c
+++ b/net/sctp/inqueue.c
@@ -170,19 +170,6 @@ next_chunk:
chunk = list_entry(entry, struct sctp_chunk, list);
- /* Linearize if it's not GSO */
- if ((skb_shinfo(chunk->skb)->gso_type & SKB_GSO_SCTP) != SKB_GSO_SCTP &&
- skb_is_nonlinear(chunk->skb)) {
- if (skb_linearize(chunk->skb)) {
- __SCTP_INC_STATS(dev_net(chunk->skb->dev), SCTP_MIB_IN_PKT_DISCARDS);
- sctp_chunk_free(chunk);
- goto next_chunk;
- }
-
- /* Update sctp_hdr as it probably changed */
- chunk->sctp_hdr = sctp_hdr(chunk->skb);
- }
-
if ((skb_shinfo(chunk->skb)->gso_type & SKB_GSO_SCTP) == SKB_GSO_SCTP) {
/* GSO-marked skbs but without frags, handle
* them normally
--
2.7.4
--
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