[PATCH infiniband-diags] query_smp.c: Avoid busy looping in process_one_recv

Hal Rosenstock
2015-04-16T14:26:24Z

From: Vladimir Koushnir <vladimirk-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Date: Thu, 16 Apr 2015 14:11:16 +0300

Today, process_one_recv calls umad_recv with zero timeout.
That means umad_recv will use non-blocking read() without polling,
In many cases, this causes busy loop.

In the fix, umad_recv is invoked with -1 (infinite timeout) and the read()
will occur only when poll exits. Also, no longer need to check for
EWOULDBLOCK.

Signed-off-by: Vladimir Koushnir <vladimirk-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
Signed-off-by: Hal Rosenstock <hal-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
---
libibnetdisc/src/query_smp.c | 2 +-
1 files changed, 1 insertions(+), 3 deletions(-)

diff --git a/libibnetdisc/src/query_smp.c b/libibnetdisc/src/query_smp.c
index 28620b4..8f179e4 100644
--- a/libibnetdisc/src/query_smp.c
+++ b/libibnetdisc/src/query_smp.c
@@ -171,9 +171,7 @@ static int process_one_recv(smp_engine_t * engine)

/* wait for the next message */
if ((rc = umad_recv(engine->umad_fd, umad, &length,
- 0)) < 0) {
- if (rc == -EWOULDBLOCK)
- return 0;
+ -1)) < 0) {
IBND_ERROR("umad_recv failed: %d\n", rc);
return -1;
}