From bdaef6e76d5fc001ca759f3ca16d6c198e6d5bd1 Mon Sep 17 00:00:00 2001
From: Steffen Maier <maier@linux.ibm.com>
Date: Fri, 21 Jul 2023 18:25:02 +0200
Subject: [PATCH] lszfcp: associative array speeds up extended SCSI device list
 a lot

The linear search in the nested loop over SCSI devices and over the indexed
array is still time consuming. So replace the indexed array with an
associative array. Build the array once outside of the nested loop by using
pathname expansion and extracting key and value from each item. Within
the SCSI device loop, an array entry is removed by means of the key without
linear search.

This commit is separate from the previous one so it is possible to revert
this one in case associative arrays would not be available and still get
the speed improvement from the indexed array in the previous commit.

Before:

$ time ~/git/s390-tools/zconf/lszfcp -De | wc -l
1036

real	0m17.605s
user	0m17.159s
sys	0m0.308s

After:

$ time ~/git/s390-tools/zconf/lszfcp -De | wc -l
1036

real	0m0.207s
user	0m0.175s
sys	0m0.032s

Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Steffen Maier <maier@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
---
 zconf/lszfcp | 53 ++++++++++++++++++++++++----------------------------
 1 file changed, 24 insertions(+), 29 deletions(-)

diff --git a/zconf/lszfcp b/zconf/lszfcp
index ce9d1170..7cd28f16 100755
--- a/zconf/lszfcp
+++ b/zconf/lszfcp
@@ -372,18 +372,28 @@ show_devices()
 		SCSI_DEVICE_LIST=`ls -d $SYSFS/devices/css0/*/*/host[0-9]*/*/`
 	fi
 
-	declare -a ZFCP_UNIT_ARRAY
+	declare -A ZFCP_UNIT_DICT
 	if $SHOW_EXTENDED; then
-		ZFCP_UNIT_ARRAY=( $SYSFS/devices/css[0-9]*/[0-9d]*/[0-9]*/0x*/0x* )
-		# remember original array size since array becomes sparse below
-		# so the array length seems to reduce but we still need to
-		# iterate the original indexe range to find all existing entries
-		ZFCP_UNIT_ARRAY_LENGTH="${#ZFCP_UNIT_ARRAY[@]}"
+		ZFCP_UNITS=false
+		for UNIT_PATH in "$SYSFS"/devices/css[0-9]*/[0-9d]*/[0-9]*/0x*/0x*; do
+			if [ "$UNIT_PATH" = "$SYSFS/devices/css[0-9]*/[0-9d]*/[0-9]*/0x*/0x*" ]; then
+				break # no match (as seen without nullglob)
+			else
+				ZFCP_UNITS=true
+			fi
+			STRIPPED_PATH=${UNIT_PATH}
+			L=${UNIT_PATH##*/}
+			STRIPPED_PATH=${STRIPPED_PATH%/*}
+			W=${STRIPPED_PATH##*/}
+			STRIPPED_PATH=${STRIPPED_PATH%/*}
+			A=${STRIPPED_PATH##*/}
+			ZFCP_UNIT_DICT["$A/$W/$L"]=${UNIT_PATH}
+		done
 	else
-		ZFCP_UNIT_ARRAY_LENGTH=0
+		ZFCP_UNITS=false
 	fi
 
-	if [ -z "$SCSI_DEVICE_LIST" ] && [ "$ZFCP_UNIT_ARRAY_LENGTH" -eq 0 ]; then
+	if [ -z "$SCSI_DEVICE_LIST" ] && ! "$ZFCP_UNITS"; then
 		if $SHOW_EXTENDED; then
 			echo "Error: No zfcp-attached SCSI devices found."
 		else
@@ -396,24 +406,9 @@ show_devices()
 		read WWPN < $SCSI_DEVICE_PATH/wwpn
 		read LUN < $SCSI_DEVICE_PATH/fcp_lun
 
-		# loop is NOP without $SHOW_EXTENDED.
-		# remove from ZFCP_UNIT_ARRAY if SCSI device exists
-		ZFCP_UNIT_PATH=""
-		for ((i=0; i < "$ZFCP_UNIT_ARRAY_LENGTH"; i++)); do
-			UNIT_PATH="${ZFCP_UNIT_ARRAY[i]}"
-			[ -z "$UNIT_PATH" ] && continue # skip unset elements
-			STRIPPED_PATH=$UNIT_PATH
-			L=${UNIT_PATH##*/}
-			STRIPPED_PATH=${STRIPPED_PATH%/*}
-			W=${STRIPPED_PATH##*/}
-			STRIPPED_PATH=${STRIPPED_PATH%/*}
-			A=${STRIPPED_PATH##*/}
-			if [ "$A/$W/$L" = "$ADAPTER/$WWPN/$LUN" ]; then
-				ZFCP_UNIT_PATH="$UNIT_PATH"
-				unset "ZFCP_UNIT_ARRAY[i]"
-				break # minor optimization, still O(n)
-			fi
-		done
+		ZFCP_UNIT_PATH="${ZFCP_UNIT_DICT[$ADAPTER/$WWPN/$LUN]}"
+		# remove from ZFCP_UNIT_DICT if SCSI device exists
+		unset "ZFCP_UNIT_DICT[$ADAPTER/$WWPN/$LUN]"
 
 		[ $LUN != ${PAR_LUN:-$LUN} ] && continue
 		[ $WWPN != ${PAR_WWPN:-$WWPN} ] && continue
@@ -426,7 +421,7 @@ show_devices()
 			[ "$SDEVSTATE" != "running" ] \
 				&& SDEVMARKER="$SDEVMARKER NotRunning"
 		else
-			# build manually because ZFCP_UNIT_ARRAY loop was NOP
+			# build manually because ZFCP_UNIT_DICT is not used
 			ZFCP_UNIT_PATH=$SYSFS/devices/css[0-9]*/[0-9d]*/$ADAPTER/$WWPN/$LUN
 		fi
 
@@ -510,8 +505,8 @@ show_devices()
 		fi
 	done
 
-	# what's left in ZFCP_UNIT_ARRAY are now units without SCSI device
-	for UNIT_PATH in "${ZFCP_UNIT_ARRAY[@]}"; do
+	# what's left in ZFCP_UNIT_DICT are now units without SCSI device
+	for UNIT_PATH in "${ZFCP_UNIT_DICT[@]}"; do
 		STRIPPED_PATH=$UNIT_PATH
 		LUN=${UNIT_PATH##*/}
 		STRIPPED_PATH=${STRIPPED_PATH%/*}