[haiku-development] Re: Old image
- From: Marcus Overhagen <marcusoverhagen@xxxxxxxx>
- To: haiku-development@xxxxxxxxxxxxx
- Date: Wed, 15 Apr 2009 18:02:02 +0200 (CEST)
Axel Dörfler <axeld@xxxxxxxxxxxxxxxx> wrote:
> Marcus Overhagen <marcusoverhagen@xxxxxxxx> wrote:
> > David McPaul <dlmcpaul@xxxxxxxxx> wrote:
> > > It was interesting how the machine worked while it was unzipping
> > > though. Lots of CPU followed by a long pause (presumably IO).
> > > While
> > > IO was going on the system was unresponsive.
> > I think this unresponsive pause is caused by the periodic execution
> > of the
> > synchronize cache command. This causes the hdd to flush it's whole
> > internal
> > buffer to disk, and can take some seconds. During that time, the hdd
> > is busy.
> >
> > I think it is a mistake to peridically execute it. It should IMO only be
> > done
> > once when shutting down the system.
>
> Synchronizing the disk really shouldn't take some seconds, and does not
> take a noticeably amount of time on any hardware I own (I really doubt
> that's the issue the Eee is suffering from). Furthermore, executing the
> sychronize should not freeze your system at all (only disk accesses).
>
> Without synchronizing the disk, you would not be able to have any kind
> of journaled file system. Since this is the status quo on all systems
> out there, I would be surprised if any current drive would take that
> long to write back a few blocks for real.
I have seen the described behaviour with a SATA disk, connected to Intel AHCI
controller,
and I also increased internal timeout from 5 to 20 sec. in the ahci driver
because of that.
Perhaps this really depends on the write cache of the hdd. Usually it should be
off,
and in this case a cache sync shouldn't take any time and complete immediatelly.
On the other hand, with a enabled 32 MB hdd write cache full of single sector
writes,
flushing could take some time.
I don't think we have code that enables/disables the cache, so it depends on
the BIOS.
Linux consider(ed?) enabling the write cache on IDE as a bad thing. Basically,
EXT3
doesn't seem to do a cache flush ever....
There is an interesting thread about this topic at
http://oss.sgi.com/archives/xfs/2002-04/threads.html#01276
regards
Marcus
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