Hello Scott, We are using Layer 2 Vswitch for the guest and the MTU size is set to 1492. None of the Ethernet frames are not being dropped by they are being delayed.
Regards, Ashwin ________________________________ From: The IBM z/VM Operating System [mailto:IBMVM@LISTSERV.UARK.EDU] On Behalf Of Scott Rohling Sent: Wednesday, May 04, 2011 8:12 PM To: IBMVM@LISTSERV.UARK.EDU Subject: Re: Problem with z/Linux guest Ethernet frames (buffering ?) Just a guess, but have you checked MTU sizes? Are you using a VSWITCH for the guests or dedicated OSA? Scott Rohling On Wed, May 4, 2011 at 5:15 PM, Bhemidhi, Ashwin <ashw...@ti.com<mailto:ashw...@ti.com>> wrote: Hello all, Recently we started noticing on few of our Linux guest that Ethernet frames were being delayed up to 25 seconds from the time they were sent to the time the guest received them. The frames are Ethernet LLC keep alive polls (layer 2 poll) that are sent by a Cisco SNA switch router every 30 secs. Both the router and the Linux guest are in the same LAN. Looking at the ethereal traces captured on the guest. During normal operation the keep alive Frames are being sent every 30 secs and the z/Linux guest responds to the poll with in 60 micro seconds. But few times we noticed that the frames were being delayed up to 25 seconds (total time from the previous poll is 30+25) after the router sends the poll frame to the time the Linux guest receives them. This is causing the keep alive timer ( 9 secs = 1 sec X 8 retries) to expire and disconnect sessions. The Linux guest eventually receives the frames including the retires all at the same but by that time the sessions are dropped the router. It appears that the frames are being buffered and are delayed by the guest receives them. We for sure know that the router is sending the poll every 30 seconds but some were some how the frames were buffered (?) for 25 secs before being delivered to the guest. I am trying to figure at which layer the delay was being introduced. Are there any other traces that I can turn on z/VM to diagnose the problem? Were do I start looking at? z/VM LPAR is a small one running 8 guest with 80MB memory and 16MB and 48MB vdisk on a z10 IFL utilization : 2% X 2 IFLS, Central Storage : 95% 768 MB, XSTORE : 97% 256MB, PAGE : 12% X 2 3390-3 page DASD. Paging/Spooling activity: 0/s (most of the times) Thank you, Ashwin Bhemidhi
