High roll wait time

Question

For my below crm transaction for a perticular user the response time is ~18000 ms out of which 15130 is roll time. Memory used is 16 MB.
"BSPWDWCC_SLS_HOME  SAPMHTTP  /sap/bc/bsp/sap/CRM_UI_PORTAL/B"
Roll time
Out                 5  ms
In                  5  ms
Wait           15,130  ms
Where is causing this roll wait ? What memory is not sufficient ? What to look at ?
In st02
roll buffer max used is 25% ,
page buffer max used is 10%.
EM max used 50%.
No swaps for above.
My user memory settings are as below:
ztta/roll_area                              9000000
ztta/roll_first                             1
ztta/roll_extension                         4000000000
thank you
Laxmi

Answer 1

Thank you Shyam,Krishna.
I checked another similar instance again today with high wait time.  Most of the time was wait time. There were NO RFC RECORD. just http record with most of it being on the server (Remote exec. time ~ 16 534 ms).
Now i assume calling time = gate way time + remote exec time. So as most of it was on the server I can rule out network.
I checked st03 and rfc times were really small. Also we have plenty of wps .. ~ 90. So not sure why still the high wait time. Also stad does not give any RFC record. If this was rfc will it now show up ?
I have given below the details. Am I missing some thing ?
Response time           16,546 ms
Wait for work process          5 ms
Processing time            1,155 ms
Load time                     28 ms
Generating time                0 ms
Roll (in+wait) time       15,016 ms
Database request time        341 ms
Enqueue time                   0 ms
Roll time   Out                 5  ms
             In                  3  ms
             Wait           15,013  ms
NO RFC SUB RECORD
HTTP Records
as Server
Number      Connections                            1
                   Destinations                           1
                   Calls                                       1
Time     Calling                            16,540   ms
            Remote execution          16,534   ms
            Idle                                 219   ms
HTTP Server connection record
Connection-Id          4B7CAADEF5DA00A7E10080000A68F456
Communication step     Send/Receive
Timestamp              20100218 155216 EST
Host                   sappc003
Port                   8031
Path                   /sap/bc/bsp/sap/crm_ui_frame/BSPWDApplication.do
Status phrase          OK
Status code              200
Protocol               HTTP
Method                 GET