I've seen this a lot. You need to find the real bottleneck. Are
you equiped?
Mark Wheeler wrote:
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
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note:If you can't measure it, I'm just not interested
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