Comment 512 for bug 620074
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7020100
(Get the code!)
#496:
yes the patch mentioned on phoronix IS the one from #488, and as reported by several it seems to improve IO latency (at the cost of throughput?) but falls short of completely preventing stalls. Strange thing for me is, the problems seemingly increase with uptime... besides i noticed some rogue flash-btrfs-1 threads causing 1MiB/s avg disk writing (uptime > 2 days, even after bringing down services causing heavy IO).. posted a blktrace of that to the linux-btrfs ml but no answer yet ^^
Wow this one's a tricky one.
One thing i noticed a few kernel revisions back that might be relevant: there were a lot of processes in IOWAIT state (result of compiling packages, BOINC, munin-graph, ntop... and then some) and i wanted to priorize a single process so i issued a ionice -p xxx -c1 -n0 (realtime: prio 0). What i expected was that that process would instantly get its IO through and pick up work - alas it took SEVERAL MINUTES before it did. That really wtfed me.. Is this broken by design? Shouldn't iorenicing take effect immediately?