Re: [Jfs-discussion] Performance of jfs

[Dave K. <sh...@au...>]

On Saturday 24 August 2002 11:30, szonyi calin wrote:
> Hi
> Just switched my root partition from ext2 to
> jfs.
>
> Problems:
> 1.Jfs is much slower when copying big files.
>
> Description:
> If a copy a big file from the cd at the beginning
> the speed is about 2.5MB/s on jfs compared to
>  3.5(4)MB/s on ext2. Then as copying continues the
> speed decreases to 1.5MB/s. The cdrom is mostly idle
> while the data is written to the disk.
> Harddrive is UDMA33. These numbers are from mc.
>
> Any chance of improving this performance ?

Yes, there is a good chance.  We haven't had the opportunity to put as 
much work into performance tuning as we would have liked.  Our focus so 
far has been on function and stability.  I plan to put a lot more work 
into performance in the next few months.

> If you want, i can provide more information about
> my computer.

Thanks, but I think I'll be able to reproduce something similar myself.  
I may get back to you later if I don't get the same results, or if I 
have a fix that I think will give you better results.  I can't promise 
a real quick turnaround right now, though.

> 2. It seems that the journal is updated once every
> five seconds. Is there a way to change this ?
> Is there a way to update the journal more often
> when the system is loaded and not so often when
> the system is idle ?

The five seconds is the interval that the kupdated daemon runs.  I think 
it is tunable through a sysctl, but I don't know the details.  The 
problem is probably due to JFS having an ordered journal.  The data 
pages need to be written before the inode's metadata.  The solution is 
either to be more aggressive about flushing file data to disk (this can 
be done by actively pushing data to disk if we detect that the writing 
is being done sequentially) or through a more asynchronous inode commit 
mechanism.

> Thanks
> Bye
> Calin

Thank you!
Shaggy
-- 
David Kleikamp
IBM Linux Technology Center