Re: [PATCH v7 00/31] Introduce discontiguous frames management

[Stefano Brivio <sbrivio@redhat.com>]

On Mon, 23 Jun 2025 13:06:04 +0200
Laurent Vivier <lvivier@redhat.com> wrote:

> This series introduces iov_tail to convey frame information
> between functions.
> 
> This is only an API change, for the moment the memory pool
> is only able to store contiguous buffer, so, except for
> vhost-user in a special case, we only play with iovec array
> with only one entry.
> 
> v7:
>     - Add a patch to fix comment style of 'Return:'
>     - Fix ignore_arp()/accept_arp()
>     - Fix coverity error
>     - Fix several comments

I was about to apply this without 1/31 (I applied the v2 of it you sent
outside of this series instead, which is actually up to date) and with
the minor comment fix to 31/31... but the test perf/passt_vu_tcp fails
rather consistently now (and I triple checked without this series):

- "TCP throughput over IPv6: guest to host" with MTU 1500 and 9000
  bytes now reports between 0 and 0.6 Gbps. The guest kernel prints a
  series of two messages with ~1-10 µs interval:

[   21.159827] TCP: out of memory -- consider tuning tcp_mem
[   21.159831] TCP: out of memory -- consider tuning tcp_mem

- "TCP throughput over IPv4: guest to host" never reports 0 Gbps, but
  the throughput figure for large MTU (65520 bytes) is very low (5.4
  Gbps in the last run). Here I'm getting four messages:

[   40.807818] TCP: out of memory -- consider tuning tcp_mem
[   40.807829] TCP: out of memory -- consider tuning tcp_mem
[   40.807829] TCP: out of memory -- consider tuning tcp_mem
[   40.807830] TCP: out of memory -- consider tuning tcp_mem

- on the reverse direction, "TCP throughput over IPv4: host to guest"
  (but not with IPv6), the iperf3 client gets SIGSEGV, but not
  consistently, it happened once out of five times.

To me it smells a bit like we're leaking virtqueue slots but I looked
again at the whole series and I couldn't find anything obvious... at
least not yet.

UDP tests never fail and the throughput is the same as before.

I'm stopping here for the moment, let me know if I should run more
tests or anything.

By the way, I'm running just those tests by enclosing the rest of
the sequence in test/run in a dummy function, say:

---
diff --git a/test/run b/test/run
index f73c311..97b96a4 100755
--- a/test/run
+++ b/test/run
@@ -67,6 +67,7 @@ run() {
 	perf_init
 	[ ${CI} -eq 1 ]   && video_start ci
 
+dont() {
 	setup build
 	test build/all
 	test build/cppcheck
@@ -178,6 +179,8 @@ run() {
 	test perf/pasta_udp
 	test passt_in_ns/shutdown
 	teardown passt_in_ns
+}
+	VALGRIND=0
 
 	VHOST_USER=1
 	setup passt_in_ns
---

...you could also pass the setup steps plus test to ./run, but you would
need to set VHOST_USER=1 as well.

-- 
@@ -67,6 +67,7 @@ run() {
 	perf_init
 	[ ${CI} -eq 1 ]   && video_start ci
 
+dont() {
 	setup build
 	test build/all
 	test build/cppcheck
@@ -178,6 +179,8 @@ run() {
 	test perf/pasta_udp
 	test passt_in_ns/shutdown
 	teardown passt_in_ns
+}
+	VALGRIND=0
 
 	VHOST_USER=1
 	setup passt_in_ns
---

...you could also pass the setup steps plus test to ./run, but you would
need to set VHOST_USER=1 as well.

-- 
Stefano