[dpdk-dev] [RFC PATCH] test/distributor: fix burst flush on worker quit

[Stanislaw Kardach]

While working on RISC-V port I have encountered a situation where worker
threads get stuck in the rte_distributor_return_pkt() function in the
burst test.
After investigation some of the threads enter this function with
flag RTE_DISTRIB_GET_BUF set in the d->retptr64[0]. At the same time
main thread has already passed rte_distributor_process() so nobody will
clear this flag and hence workers can't return.

What I've noticed is that adding a flush just after the last _process(),
similarly to how quit_workers() function is written in the
test_distributor.c fixes the issue.
Additionally the issue disappears when I remove the rdtsc delay code
inside the rte_distributor_request_pkt().
However I can't get this to reproduce on x86 (even with SIMD forced
off) and with artificial delays, which is why I wonder whether I'm not
actually hiding some other issue.

Looking at the implementation of the distributor, it is based on
__atomic_* builtins and the only platform related bit in the fast-path
is the rte_rdtsc() and rte_pause(). There may be some issues in the
toolchain (I've tried so far with the Ubuntu one - 10.2.0-8ubuntu1).
I should add that all unit tests for distributor are passing so either
there's some coverage corner case or the implementation works on RISC-V.
As for RDTSC I'm using a sleep-stable time counter with 1MHz frequency
and switching to high resolution cycle counter also removes the issue
but that's the same as removing the rdtsc delay as mentioned above.

I'd love to hear from You if this fix makes any sense.

While modifying this test, I've also pulled in a fix from
test_distributor.c which ensures that each thread gets his own wakeup
packet as it's possible that when sending a burst of packets, they won't
be spread over all the workers.

Signed-off-by: Stanislaw Kardach <kda at semihalf.com>
Fixes: 7c3287a10535 ("test/distributor: add performance test for burst mode")
Cc: david.hunt at intel.com
Cc: l.wojciechow at partner.samsung.com
Cc: David Marchand <david.marchand at redhat.com>
---
 app/test/test_distributor_perf.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/app/test/test_distributor_perf.c b/app/test/test_distributor_perf.c
index b25f79a34..fdbeae6d2 100644
--- a/app/test/test_distributor_perf.c
+++ b/app/test/test_distributor_perf.c
@@ -188,13 +188,15 @@ quit_workers(struct rte_distributor *d, struct rte_mempool *p)
 	rte_mempool_get_bulk(p, (void *)bufs, num_workers);
 
 	quit = 1;
-	for (i = 0; i < num_workers; i++)
+	for (i = 0; i < num_workers; i++) {
 		bufs[i]->hash.usr = i << 1;
-	rte_distributor_process(d, bufs, num_workers);
+		rte_distributor_process(d, &bufs[i], 1);
+	}
 
 	rte_mempool_put_bulk(p, (void *)bufs, num_workers);
 
 	rte_distributor_process(d, NULL, 0);
+	rte_distributor_flush(d);
 	rte_eal_mp_wait_lcore();
 	quit = 0;
 	worker_idx = 0;
-- 
2.27.0