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query_smp.c: Avoid busy looping in process_one_recv

PATCH Applied Hal Rosenstock 2 participants 3 messages Apr 16, 2015 – Jul 3, 2015 1 message not in the archive InfiniBand

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Hal Rosenstock

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PATCH 1/1 query_smp.c: Avoid busy looping in process_one_recv

From: Vladimir Koushnir <vladimirk-VPRAkNaXOzVWk0Htik3J/[email protected]>
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/[email protected]>
Signed-off-by Hal Rosenstock <hal-VPRAkNaXOzVWk0Htik3J/[email protected]>
---
 libibnetdisc/src/query_smp.c |    2 +-
 1 files changed, 1 insertions(+), 3 deletions(-)
libibnetdisc/src/query_smp.c +1 -3
index 28620b4..8f179e4 100644
@@ -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;
 	}

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A message that is not in the archive (sent off-list or not yet received): 552FC690.1010807-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org

#2 lore raw
Quoted 10 lines · Hal Rosenstock

From: Vladimir Koushnir <vladimirk-VPRAkNaXOzVWk0Htik3J/[email protected]>
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.

Has this been tested on broken fabrics where SMAs don't respond?

I know that we should recv something (ie timed out Send) for every MAD submitted to the kernel but I seem to remember a reason we did not use a timeout. But that may have been for a previous implementation which no longer exists. I can't remember.

Ira

Quoted 12 lines
Signed-off-by Vladimir Koushnir <vladimirk-VPRAkNaXOzVWk0Htik3J/[email protected]>
Signed-off-by Hal Rosenstock <hal-VPRAkNaXOzVWk0Htik3J/[email protected]>
---
 libibnetdisc/src/query_smp.c |    2 +-
 1 files changed, 1 insertions(+), 3 deletions(-)
libibnetdisc/src/query_smp.c +0 -0
index 28620b4..8f179e4 100644

libibnetdisc/src/query_smp.c static int process_one_recv(smp_engine_t * engine) · line 177

Quoted 10 lines
libibnetdisc/src/query_smp.c +1 -3
@@ -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;
 	}

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Applied
#3 lore raw
In reply to a message not in the archive
Quoted 7 lines · Hal Rosenstock

From: Vladimir Koushnir <vladimirk-VPRAkNaXOzVWk0Htik3J/[email protected]>
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.

Quoted 6 lines

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/[email protected]>
Signed-off-by Hal Rosenstock <hal-VPRAkNaXOzVWk0Htik3J/[email protected]>

Thanks applied,
Ira

Quoted 9 lines
---
 libibnetdisc/src/query_smp.c |    2 +-
 1 files changed, 1 insertions(+), 3 deletions(-)
libibnetdisc/src/query_smp.c +0 -0
index 28620b4..8f179e4 100644

libibnetdisc/src/query_smp.c static int process_one_recv(smp_engine_t * engine) · line 177

Quoted 10 lines
libibnetdisc/src/query_smp.c +1 -3
@@ -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;
 	}

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