[mythtv-commits] Ticket #1457: Change default values for TFW_DEF_BUF_SIZE, TFW_MAX_WRITE_SIZE, and TFW_MIN_WRITE_SIZE

[MythTV]

#1457: Change default values for TFW_DEF_BUF_SIZE, TFW_MAX_WRITE_SIZE, and
TFW_MIN_WRITE_SIZE
----------------------------+-----------------------------------------------
 Reporter:  ylee at pobox.com  |       Owner:  danielk
     Type:  enhancement     |      Status:  new    
 Priority:  minor           |   Milestone:         
Component:  mythtv          |     Version:  0.19   
 Severity:  medium          |  
----------------------------+-----------------------------------------------
 Currently, the constants TFW_DEF_BUF_SIZE, TFW_MAX_WRITE_SIZE, and
 TFW_MIN_WRITE_SIZE are defined within ThreadedFileWriter.cpp as:


 {{{
 TFW_DEF_BUF_SIZE   = 2*1024*1024 (2MB)
 TFW_MAX_WRITE_SIZE = TFW_DEF_BUF_SIZE / 4 (512KB)
 TFW_MIN_WRITE_SIZE = TFW_DEF_BUF_SIZE / 8 (256KB

 }}}

 These values often prove too small to handle two HDTV recording streams
 plus a single recording stream, let alone other demands on the storage
 bandwidth like additional recording streams and mythcommflag, without
 generating IOBOUND errors.

 After extensive testing over several weeks (see http://www.gossamer-
 threads.com/lists/mythtv/users/183808?search_string=tfw_def_buf_size;#183808
 for an in-process discussion thread I started), I have found that changing
 the values to:


 {{{
 TFW_DEF_BUF_SIZE   = 64*1024*1024 (64MB)
 TFW_MAX_WRITE_SIZE = TFW_DEF_BUF_SIZE / 8 (8MB)
 TFW_MIN_WRITE_SIZE = TFW_DEF_BUF_SIZE / 256 (256KB; i.e., no change from
 current)

 }}}

 signficantly increases recording robustness. On my frontend/backend with
 CIFS-mounted video storage NAS using ext3, the above settings let me do
 the following, none possible without IOBOUND errors with the default:

  * Record two HDTV streams while watching a third.
  * Record two HDTV streams while commflagging.
  * Record three HDTV streams.
  * Delete a one-hour (~7.5GB) or smaller HDTV program while recording an
 HDTV stream.

-- 
Ticket URL: <http://svn.mythtv.org/trac/ticket/1457>
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