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fix mq-deadline for hdds

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This commit is contained in:
Simon Gardling
2026-03-30 13:21:33 -04:00
parent 9392749e66
commit eeab5de886
1 changed files with 39 additions and 4 deletions
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43
modules/hardware.nix
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@@ -23,13 +23,48 @@
hardware.enableRedistributableFirmware = true;
# HDD I/O tuning for torrent seeding workload (high-concurrency random reads).
#
# mq-deadline sorts requests into elevator sweeps, reducing seek distance.
# Aggressive deadlines (15s) let the scheduler accumulate more ops before dispatching,
# maximizing coalescence — latency is irrelevant since torrent peers tolerate 30-60s.
# fifo_batch=128 keeps sweeps long; writes_starved=16 heavily favors reads.
# 4 MiB readahead matches libtorrent piece extent affinity for sequential prefetch.
services.udev.extraRules = ''
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="1", ATTR{queue/scheduler}="mq-deadline", ATTR{queue/read_ahead_kb}="4096", ATTR{queue/nr_requests}="512"
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="1", ENV{ID_ATA_ROTATION_RATE_RPM}!="0", RUN+="${pkgs.bash}/bin/bash -c 'echo 15000 > /sys$devpath/queue/iosched/read_expire; echo 15000 > /sys$devpath/queue/iosched/write_expire; echo 128 > /sys$devpath/queue/iosched/fifo_batch; echo 16 > /sys$devpath/queue/iosched/writes_starved; echo 4096 > /sys$devpath/queue/max_sectors_kb 2>/dev/null || true'"
'';
#
# This runs as a systemd oneshot rather than udev rules because the NixOS ZFS module
# hardcodes a udev rule that forces scheduler="none" on all ZFS member partitions'
# parent disks, overriding any scheduler set via udev on the disk event.
systemd.services.hdd-io-tuning = {
description = "HDD I/O scheduler and queue tuning";
after = [
"zfs-import.target"
"systemd-udev-settle.service"
];
wantedBy = [ "multi-user.target" ];
serviceConfig = {
Type = "oneshot";
RemainAfterExit = true;
};
script = ''
for dev in /sys/block/sd*; do
[ -f "$dev/queue/rotational" ] || continue
[ "$(cat "$dev/queue/rotational")" = "1" ] || continue
# skip removable devices (USB sticks report removable=1)
[ "$(cat "$dev/removable")" = "0" ] || continue
echo mq-deadline > "$dev/queue/scheduler"
echo 4096 > "$dev/queue/read_ahead_kb"
echo 512 > "$dev/queue/nr_requests"
echo 15000 > "$dev/queue/iosched/read_expire"
echo 15000 > "$dev/queue/iosched/write_expire"
echo 128 > "$dev/queue/iosched/fifo_batch"
echo 16 > "$dev/queue/iosched/writes_starved"
echo 4096 > "$dev/queue/max_sectors_kb" 2>/dev/null || true
echo "Tuned $(basename "$dev"): mq-deadline, 4M readahead, 15s deadlines"
done
'';
};
}