1c8cc1c409
The prewarm's single big read (a ~14 min sequential pass over a 60GB remux to demux subtitles) shares the same disk/NFS as live streaming. Lower the prewarm ffmpeg processes to the Linux IDLE I/O class (ioprio_set) so that background read yields bandwidth to a user who's actually watching — the prewarm slows down under contention instead of starving playback, and runs full speed when the disk is idle. Applied only to the prewarm-only extractors (ExtractSubtitlesVTTMulti, ExtractThumbnailJPEG) via Start → setIdleIOPriority(pid) → Wait; the on-demand /sub + /thumbnail handlers keep normal priority (a user is waiting on those). Linux-only syscall behind a build tag; a no-op stub elsewhere. Best-effort — errors ignored, never required for correctness. Verified: the prewarm ffmpeg shows 'idle' under ionice -p; on-demand stays normal.
25 lines
1 KiB
Go
25 lines
1 KiB
Go
//go:build linux
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package mediainfo
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import "syscall"
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// Linux I/O priority (ioprio) constants. The 16-bit ioprio value packs a class
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// in the top 3 bits (shift 13) and a class-data nibble below it; the IDLE class
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// takes no data.
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const (
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ioprioWhoProcess = 1 // IOPRIO_WHO_PROCESS
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ioprioClassIdle = 3 // IOPRIO_CLASS_IDLE
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ioprioClassShift = 13
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)
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// setIdleIOPriority best-effort lowers a process's I/O scheduling class to IDLE,
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// so a long background read (the subtitle prewarm of a huge remux — a single
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// ~14 min sequential read of a 60GB file over NFS) yields disk/NFS bandwidth to
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// foreground work like live streaming. Linux-only; on kernels or filesystems
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// that don't honor ioprio this simply has no effect. Errors are intentionally
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// ignored — it's an optimization, never required for correctness.
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func setIdleIOPriority(pid int) {
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ioprio := ioprioClassIdle << ioprioClassShift // IDLE class, data 0
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_, _, _ = syscall.Syscall(syscall.SYS_IOPRIO_SET, uintptr(ioprioWhoProcess), uintptr(pid), uintptr(ioprio))
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}
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