linux-kernel - Re: Linux 2.6.29

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Date:	Fri, 03 Apr 2009 15:57:52 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Mark Lord <lkml@....ca>
CC:	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>,
	Jens Axboe <jens.axboe@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>, tytso@....edu,
	drees76@...il.com, jesper@...gh.cc,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.29

Mark Lord wrote:
> Lennart Sorensen wrote:
>>
>> Well the system is setup like this:
>>
>> Core 2 Quad Q6600 CPU (2.4GHz quad core).
>> Asus P5K mainboard (Intel P35 chipset)
>> 6GB of ram
>> PVR500 dual NTSC tuner pci card
> ..
>> So the behaviour with cfq is:
>> Disk light seems to be constantly on if there is any disk activity.  
>> iotop
>> can show a total io of maybe 1MB/s and the disk light is on constantly.
> ..
> 
> Lennart,
> 
> I wonder if the problem with your system is really a Myth/driver issue?
> 
> Curiously, I have a HVR-1600 card here, and when recording analog TV with
> it the disk lights are on constantly.  The problem with it turns out to
> be mythbackend doing fsync() calls ten times a second.
> 
> My other tuner cards don't have this problem.
> 
> So perhaps the PVR-500 triggers the same buggy behaviour as the HVR-1600?
> To work around it here, I decided to use a preload library that replaces
> the frequent fsync() calls with a more moderated behaviour:
> 
>   http://rtr.ca/hvr1600/libfsync.tar.gz
> 
> Grab that file and try it out.  Instructions are included within.
> Report back again and let us know if it makes any difference.
> 
> Someday I may try and chase down the exact bug that causes mythbackend
> to go fsyncing berserk like that, but for now this workaround is fine.

mythtv/libs/libmythtv/ThreadedFileWriter.cpp is a good place to start 
(Sync method... uses fdatasync if available, fsync if not).

mythtv is definitely a candidate for sync_file_range() style output, IMO.

	Jeff


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