Messages in this thread | | | Date | Thu, 22 Nov 2007 14:41:06 +1100 | From | David Chinner <> | Subject | Re: [PATCH 2/9]: Reduce Log I/O latency |
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On Wed, Nov 21, 2007 at 08:57:27PM -0600, Matt Mackall wrote: > On Thu, Nov 22, 2007 at 12:12:14PM +1100, David Chinner wrote: > > In all the cases that I know of where ppl are using what could > > be considered real-time I/O (e.g. media environments where they > > do real-time ingest and playout from the same filesystem) the > > real-time ingest processes create the files and do pre-allocation > > before doing their I/O. This I/O can get held up behind another > > process that is not real time that has issued log I/O. > > > > Given there is no I/O priority inheritence and having log I/O stall > > will stall the entire filesystem, we cannot allow log I/O to > > stall in real-time environments. Hence it must have the highest > > possible priority to prevent this. > > I've seen PVRs that would be upset by this. They put media on one > filesystem and database/apps/swap/etc. on another, but have everything > on a single spindle. Stalling a media filesystem read for a write > anywhere else = fail.
Sounds like the PVR is badly designed to me. If a write can cause a read to miss a playback deadline, then you haven't built enough buffering into your playback application.
Cheers,
Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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