Hi ,
just to give some feedback on 2.6.24-rc1. For some time I am tracking IO/writeback problems that hurt system responsiveness big-time. I tested Peters stuff together with Fenguangs additions and it looked promising. Therefore I was very happy to see Peters stuff going into 2.6.24 and waited eagerly for rc1. In short, I am impressed. This really looks good. IO throughput is great and I could not reproduce the responsiveness problems so far.
Below are a some numbers of my brute-force I/O tests that I can use to bring responsiveness down. My platform is a HP/DL380g4, dual CPUs, HT-enabled, 8 GB Memory, SmartaArray6i controller with 4x72GB SCSI disks as RAID5 (battery protected writeback cahe enabled) and gigabit networking (tg3). User space is 64-bit RHEL4.3
I am basically doing copies using "dd" with 1MB blocksize. Local Filesystem ist ext2 (noatime). IO-Scheduler is dealine, as it tends to give best results. NFS3 Server is a Sun/T2000/Solaris10. The tests are:
dd1 - copy 16 GB from /dev/zero to local FS
dd1-dir - same, but using O_DIRECT for output
dd2/dd2-dir - copy 2x7.6 GB in parallel from /dev/zero to local FS
dd3/dd3-dir - copy 3x5.2 GB in parallel from /dev/zero lo local FS
net1 - copy 5.2 GB from NFS3 share to local FS
mix3 - copy 3x5.2 GB from /dev/zero to local disk and two NFS3 shares
I did the numbers for 2.6.19.2, 2.6.22.6 and 2.6.24-rc1. All units are MB/sec.
test 2.6.19.2 2.6.22.6 2.6.24.-rc1
----------------------------------------------------------------
dd1 28 50 96
dd1-dir 88 88 86
dd2 2x16.5 2x11 2x44.5
dd2-dir 2x44 2x44 2x43
dd3 3x9.8 3x8.7 3x30
dd3-dir 3x29.5 3x29.5 3x28.5
net1 30-33 50-55 37-52
mix3 17/32 25/50 96/35 (disk/combined-network)
Some observations:
- single threaded disk speed really went up wit 2.6.24-rc1. It is now even better than O_DIRECT
- O_DIRECT took a slight hit compared to the older kernels. Not an issue for me, but maybe others care
- multi threaded non O_DIRECT scales for the first time ever !!!! Almost no loss compared to single threaded !!!!!!
- network throughput took a hit from 2.6.22.6 and is not as repeatable. Still better than 2.6.19.2 though
What actually surprises me most is the big performance win on the single threaded non O_DIRECT dd test. I did not expect that :-) What I had hoped for was of course the scalability.
So, this looks great and most likely I will push 2.6.24 (maybe .X) into my environment.
Happy weekend
Martin
------------------------------------------------------
Martin Knoblauch
email: k n o b i AT knobisoft DOT de
www: http://www.knobisoft.de
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