Public bug reported: This issue seems similar to https://bugs.launchpad.net/ubuntu/+source /linux-source-2.6.22/+bug/131094, however I created a new bug because the processes I am running are more CPU intensive than IO intensive.
Due my lack of understanding of the disk buffer cache, I will probably need some handholding. I'm running a pretty heavy-weight process (Rails tests) that involves several worker processes, in an effort to parallelize the runs. To measure the performance impacts, I run hdparm -T /dev/sda to give me the cached read performance. Note that the disk IO is not being measured, but the disk cache IO is. It works very well on my work machine (8-core Mac Pro running Ubuntu with 8GB of RAM). The baseline is: honk4:~ $ sudo hdparm -T /dev/sda /dev/sda: Timing cached reads: 13224 MB in 2.00 seconds = 6616.86 MB/sec In the middle of the test run: honk4:~ $ sudo hdparm -T /dev/sda /dev/sda: Timing cached reads: 4598 MB in 2.00 seconds = 2299.26 MB/sec After the test run is finished, hdparm returns back to the original result. The test suite ran 8 workers. --- On my laptop, it is a different story. I have a quad core machine with 3.4GB of RAM. The test suite runs 4 workers. Now the baseline is around 6000 MB/sec. When I run the suite, it ranges between 2000-5000 MB/sec. After the suite is finished, the performance keeps on dropping. It finally goes down to ~ 350 MB/sec. What is strange is around 30 minutes later, hdparm -T goes back to 6000 MB/sec. I tried sudo sh -c 'sync; echo 3 > /proc/sys/vm/drop_caches', but it does not seem to help. --- Having less worker processes decreases the severity and duration of the slowness. ProblemType: Bug DistroRelease: Ubuntu 10.04 Package: linux-image-2.6.32-21-generic 2.6.32-21.32 Regression: No Reproducible: Yes ProcVersionSignature: Ubuntu 2.6.32-21.32-generic 2.6.32.11+drm33.2 Uname: Linux 2.6.32-21-generic i686 NonfreeKernelModules: nvidia wl AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.21. AplayDevices: **** List of PLAYBACK Hardware Devices **** card 0: Intel [HDA Intel], device 0: STAC92xx Analog [STAC92xx Analog] Subdevices: 0/1 Subdevice #0: subdevice #0 Architecture: i386 ArecordDevices: **** List of CAPTURE Hardware Devices **** card 0: Intel [HDA Intel], device 0: STAC92xx Analog [STAC92xx Analog] Subdevices: 2/2 Subdevice #0: subdevice #0 Subdevice #1: subdevice #1 AudioDevicesInUse: USER PID ACCESS COMMAND /dev/snd/controlC0: btakita 2154 F.... pulseaudio /dev/snd/pcmC0D0p: btakita 2154 F...m pulseaudio CRDA: Error: [Errno 2] No such file or directory Card0.Amixer.info: Card hw:0 'Intel'/'HDA Intel at 0xf6fdc000 irq 21' Mixer name : 'IDT 92HD71B7X' Components : 'HDA:111d76b2,10280250,00100302' Controls : 21 Simple ctrls : 15 CheckboxSubmission: 0284e32f1bd1ad9229c88cd83df0f446 CheckboxSystem: d00f84de8a555815fa1c4660280da308 Date: Mon Apr 19 11:42:04 2010 HibernationDevice: RESUME=UUID=43e19dcb-222a-41b1-b5ed-d0dcb1373c00 MachineType: Dell Inc. Precision M4400 PccardctlIdent: Socket 0: no product info available PccardctlStatus: Socket 0: no card ProcCmdLine: BOOT_IMAGE=/boot/vmlinuz-2.6.32-21-generic root=UUID=f6ca8c66-fac4-4b0e-8fe5-545b866ec315 ro elevator=noop quiet splash ProcEnviron: PATH=(custom, user) LANG=en_US.UTF-8 SHELL=/bin/bash RelatedPackageVersions: linux-firmware 1.34 SourcePackage: linux WifiSyslog: Apr 19 10:35:56 saturn kernel: [ 2573.965068] dell-wmi: Unknown key ffd0 pressed Apr 19 11:22:24 saturn kernel: [ 5361.495008] dell-wmi: Unknown key ffd1 pressed WpaSupplicantLog: dmi.bios.date: 02/13/2009 dmi.bios.vendor: Dell Inc. dmi.bios.version: A12 dmi.board.name: 0NY980 dmi.board.vendor: Dell Inc. dmi.chassis.type: 8 dmi.chassis.vendor: Dell Inc. dmi.modalias: dmi:bvnDellInc.:bvrA12:bd02/13/2009:svnDellInc.:pnPrecisionM4400:pvr:rvnDellInc.:rn0NY980:rvr:cvnDellInc.:ct8:cvr: dmi.product.name: Precision M4400 dmi.sys.vendor: Dell Inc. ** Affects: linux (Ubuntu) Importance: Undecided Status: New ** Tags: apport-bug filesystem i386 lucid needs-upstream-testing -- Running processor intensive processes slows down disk buffer cache long after processes are completed https://bugs.launchpad.net/bugs/566841 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs