Hi Stan, Thanks for your reply. I will bring this to the attention of the system administrator (I have root access but I don't think they'll appreciate me installing a new kernel on my own).
I've just discovered that a similar issue can also occur with pure compute tasks (no I/O at all). If I run 8 of those in parallel, some of them will run on logical CPUs of the same physical CPU, and those are slower than the ones that get a physical CPU to themselves. Since there are enough physical CPUs available, I don't believe the scheduler should do this. Hopefully upgrading the kernel will resolve this as well. Thanks, Sven -----Original Message----- From: Stan Hoeppner [mailto:s...@hardwarefreak.com] Sent: vrijdag 4 maart 2011 16:10 To: debian-user@lists.debian.org Subject: Re: Hyperthreading problem with IRQ handling and scheduling Sven Groot put forth on 3/3/2011 11:28 PM: Hello Sven, > I am using a cluster of machines running Debian 5.0.4, kernel > 2.6.26-2-amd64. These machines have dual Intel Xeon E5530 2.4GHz CPUs, > which are quad-core CPUs with hyperthreading. So that means each > machine has 8 physical CPUs and a total of 16 logical CPUs. > I have run into an apparent issue with the kernel scheduler. Under the > circumstances described below, the scheduler will run two tasks on two > logical CPUs of the same physical CPU, even if all the remaining > physical CPUs are idle. This obviously causes a large slowdown for these tasks. <snip> Two things. First, you're running Debian kernel 2.6.26 which, IIRC, doesn't have all the scheduler patches required for both mutli-core and HT support, or simply doesn't have them all enabled, which is the cause of your problem. The following must all be set. You need a new kernel. CONFIG_SCHED_SMT CONFIG_SCHED_MC 1. Install the latest Debian prepackaged lenny-backport kernel on each cluster node: linux-image-2.6.32-bpo.5-amd64_2.6.32-30~bpo50+1_i386.deb http://backports.debian.org/Instructions/ If the nodes don't have direct internet access, preventing installation via apt-get or aptitude, then download the .deb package, copy it to each machine via scp/ftp/nfs/etc, and install it via dpkg: dpkg -i /full/path/to/linux-image-2.6.32-bpo.5-amd64_2.6.32-30~bpo50+1_i386.deb I've never installed a backport package directly via dpkg. You may need an additional switch or two. Others here can answer this. 2. Download the 2.6.37.2 vanilla source from: http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.37.2.tar.bz2 Follow the build instructions here: http://kernel-handbook.alioth.debian.org/ch-common-tasks.html to create a kernel image with the options and modules you need, and none you don't, and to create a kernel deb package. Copy the .deb to each cluster node and perform: dpkg -i /full/path/to/linux-image-2.6.37.2-custom.1.0_amd64.deb Second, you may want to ask about this on lkml as well, as far more expertise in this area of the kernel resides there. Installing a new kernel will solve the bulk of your problem. To fine tune the performance per core/thread afterward you'll need assistance from kernel devs on lkml. Hope this points you in the right direction. -- Stan -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/4d709039.80...@hardwarefreak.com -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/001201cbda3c$99e92f00$cdbb8d00$@gmail.com
