Hi, at the moment, I've got the following I/O stack on my system: filesystems (ext4 and swap) lvm2 dm-crypt md raid 5 physical disks other than that, I'm using a quadcore Athlon II X4 640 and 8 GB RAM. I'm using a vanilla kernel (I/O scheduler: CFS). I'm experiencing unresponsiveness and a general system slowdown when I'm unpacking big archives or building a big packages (during builds I'm only using max 2 cores). To counter this, I've been experimenting with nice and ionice. Unfortunately, ionice -c3 before big I/O traffic doesn't seem to make any difference. The responsiveness is still really bad at times. I've been googling in reading in forums quite a lot and there seems to be an longstanding issue in the linux kernel (https://bugzilla.kernel.org/show_bug.cgi?id=12309) that hasn't been resolved for years. Huge discussion threads seem to deal with this issue: http://forums.gentoo.org/viewtopic-t-793263-start-100-postdays-0-postorder-asc-highlight-.html?sid=175e371c81170f23e7116626a6b26755 https://bbs.archlinux.org/viewtopic.php?id=93960 Some are suggesting to use different schedulers (BFQ, BFS). Others are tinkering with the kernel I/O parameters. Most of these counter measures seem to have little or no effect to others in follow-ups postings. At this point I could have said: "Linux doesn't handle I/O well" and grudgingly live with it. However, a different post caught my attention: http://www.saout.de/pipermail/dm-crypt/2009-October/000329.html Christian Pernegger did some tests in which he changed the vfs layers. My layer (dm-crypt on top of md) came out worst in his tests. dm-crypt directly on top of the physical disk seemed to be the best option. Other people suggested that using dm-crypt renders the I/O scheduler of the kernel useless. Since Christian Pernegger's post in 2009, some things have changed: dm-crypt has become multi-threaded the linux kernel has changed (VFS, CFS) So my questions are: - does the position of dm-crypt in the vfs layer affect I/O performance significantly nowadays? - is there an explanation for that? - can anyone suggest a diagnosis on my system that would prove or disprove that dm-crypt is in the wrong position in the vfs stack before I start reordering it on my system _______________________________________________ dm-crypt mailing list dm-crypt@xxxxxxxx http://www.saout.de/mailman/listinfo/dm-crypt
