Package: mdcfg Severity: wishlist Tags: d-i patch Hello,
from benchmarks in bug #722898 it has emerged that blockdev-wipe is approx. 20% faster when the guaranteed md resync speed [*] is zero, meaning that userspace I/O will always be scheduled ahead of resync I/O. The default setting enforces 1000kB/s resync I/O before userspace requests are honoured. Although setting aside 1MB/s for resync doesn't sound like much, this can translate to a loss of 10-20MB/s for userspace requests, presumably due to competition for disk read/write heads. I assume that changing this setting will also bring speed gains for the package installation phase, that's why I'm proposing a patch (cf. attachment) to alter the setting whenever md devices are detected. Bottom line: The proposed patch gives userspace full I/O priority, but md raid resync will use whatever I/O bandwith that is not required by userspace. Cheers, Thiemo [*] set via /proc/sys/dev/raid/speed_limit_min -- System Information: Debian Release: 7.1 APT prefers stable-updates APT policy: (500, 'stable-updates'), (500, 'proposed-updates'), (500, 'stable') Architecture: amd64 (x86_64) Foreign Architectures: i386 Kernel: Linux 3.2.0-4-amd64 (SMP w/4 CPU cores) Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8) Shell: /bin/sh linked to /bin/dash
>From 086c51a14dbbc8868461c41820d712b9158994ae Mon Sep 17 00:00:00 2001 From: Thiemo Nagel <[email protected]> Date: Tue, 17 Sep 2013 14:51:59 +0200 Subject: [PATCH] Set guaranteed resync speed to zero to accelerate install blockdev-wipe is approx. 20% faster that way (cf. bug #722898) and I'd expect that there'll be similar improvements in the package installation phase. --- mdcfg.sh | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mdcfg.sh b/mdcfg.sh index 506e58c..2e3c9f7 100755 --- a/mdcfg.sh +++ b/mdcfg.sh @@ -430,6 +430,11 @@ if ! [ -e /proc/mdstat ] || ! [ -d /dev/md ]; then exit 0 fi + # Speed up installation by de-priorizing (not stopping) array resync + if [ -w /proc/sys/dev/raid/speed_limit_min ]; then + echo 0 > /proc/sys/dev/raid/speed_limit_min + fi + # Try to detect MD devices, and start them # mdadm will fail if /dev/md does not already exist mkdir -p /dev/md -- 1.7.10.4
