More info: FTP GET's of this cached 256MB file to /dev/null have run as fast as 205 MB/sec w/ MTU=32760 over hipersocket interfaces, and 168 MB over virtual CTCs. FTP PUT's are a different matter: hipersocket or CTC doesn't make a difference. The higher MTU size, the slower the transfer rate (from 90-100 MB/sec w/ MTU=16376 down to 10-15 MB/sec for MTU=32084. At MTU=32085, performance drops off a cliff, down to 400 KB/sec.
So, one problem appears to be related to FTP PUT performance with large MTU sizes. In the process of investigating this alleged "hipersocket performance problem" (as reported by our Linux support person up four chains of management), I discovered an interesting issue with scp. It shows very limitted sensitivity for interface type, MTU size, or direction of movement), however I can't get it to run faster than 8 MB/sec (25 times slower than FTP GET). I'm using scp between two virtual Linux machines running on a 1-IFL system, so thought initially it may have been CPU contention (no hardware crypto on this box), yet CPU util was less than 5% on each machine. What I did see was the sending side doing a lot of disk I/O, something I don't see with FTP. Is it possible that scp reads from disk, bypassing the cache? Linux version 2.6.5-7.276-s390x Best regards, Mark > > Greetings all, > > I've been using real hipersockets for a couple years now. Recently a > significant performance problem with SLES 9 and large MTU sizes was brought > to my attention. I've been using MTU=32760. I set up a test to illustrate > the problem. I built a 256 MB file on one zLinux guest (running under z/VM > 5.2 on a z9-109), with enough storage defined so the file could be > completely cached. I then FTP'd it to /dev/null on another server over a > hipersocket connection. Here's what I observed: > SLES8-to-SLES8, MTU=8184, ~75 MB/sec > SLES8-to-SLES8, MTU=32760, ~100 MB/sec (as high as 132 MB/sec) > SLES8-to-SLES9, MTU=32760, ~100 MB/sec > z/VM-to-SLES9, MTU=32760, ~100 MB/sec (from file on VDISK to /dev/null) > z/OS-to-SLES9, MTU=32760, ~25 MB/sec (from disk cache on z/OS) > SLES9-to-SLES9, MTU=8184, ~75 MB/sec > SLES9-to-SLES9, MTU=32760, ~400 KB/sec (not MegaBytes, KiloBytes!) > > Has anyone else seen this? > > I use 32760 on my hipersocket links so as to be consistent with the 32760 > MTU size used on CTC links to other processors owned by my z/VM TCPIP > machine, which is used as the gateway between Linux guests on one machine > and z/OS on the other machines. > > Best regards, > Mark Wheeler, 3M Company > > ---------------------------------------------------------------------- > For LINUX-390 subscribe / signoff / archive access instructions, > send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit > http://www.marist.edu/htbin/wlvindex?LINUX-390 > > ---------------------------------------------------------------------- > For LINUX-390 subscribe / signoff / archive access instructions, > send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit > http://www.marist.edu/htbin/wlvindex?LINUX-390 > ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390