[mythtv-commits] Ticket #9458: [PATCH] posix_fadvice usage

MythTV noreply at mythtv.org
Fri May 13 21:37:49 UTC 2011


#9458: [PATCH] posix_fadvice usage
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 Reporter:  jiri.fojtasek@…             |          Owner:  danielk
     Type:  Patch - Bug Fix             |         Status:  closed
 Priority:  minor                       |      Milestone:  0.25
Component:  MythTV - General            |        Version:  Trunk Head
 Severity:  medium                      |     Resolution:  Fixed
 Keywords:                              |  Ticket locked:  0
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--version Output:


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Changes (by danielk):

 * status:  assigned => closed
 * resolution:   => Fixed


Comment:

 Most of the issues here were dealt with by [e4c5909]. The rest would seem
 to be a bad idea for the same reason previous fadvise patches were a bad
 idea. First, linux interprets the DONTNEED calls globally, so if one
 application says it won't need the data and another says it will, the data
 can get thrown out of cache repeatedly. The other problem is that WILLNEED
 doesn't tell the OS to start reading the data in the background so a
 future read will execute more quickly, it actually blocks while reading in
 the entire amount of data that we're telling it we will need in the
 future. All this means the only really useful thing we can do with fadvise
 is to issue the SEQUENTIAL one, and there are a couple cases where it
 makes sense to do a small WILLNEED just to avoid starting playback and
 then pausing (it's better to just take a few milliseconds longer start
 delivering frames than to deliver a few and then pause for a few
 milliseconds.)

-- 
Ticket URL: <http://code.mythtv.org/trac/ticket/9458#comment:5>
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