Subject: Re: Interactive responsiveness under heavy I/O load
To: None <firstname.lastname@example.org>
From: John Goerzen <email@example.com>
Date: 01/26/2004 17:16:19
Thanks for your reply and explanation, Thor. I have a couple of
On 2004-01-26, Thor Lancelot Simon <firstname.lastname@example.org> wrote:
> On Mon, Jan 26, 2004 at 04:30:08PM +0000, John Goerzen wrote:
> The new I/O sorting algorithm in -current should make this significantly
> better. I am hoping that it can become the default for 2.0.
If I were to upgrade to current, how would I enable this sorting
algorithm on my system?
>> It seems like when this problem occurs, an I/O scheduler somewhere is
>> starving everything but the big writing process of resources. But I
>> have no idea if this is tweakable somewhere, or how to go about fixing
> You say later that you're using softdep. The likely problem is an
> interaction of softdep and the questionable behaviour of the delayed
> write scheduling code (the "smooth-sync" or "syncer") code that was
> imported along with softdep.
> So there is a light at the end of the tunnel. If you want immediate
> relief, turning off softdep should make your system's interactive
> performance more predictable, though it will probably make your
> I/O itself slower.
Significantly. One of the first things I did with my new NetBSD system
was to untar pkgsrc.tar.gz. It was S L O W. I didn't make formal
benchmarks, but after turning on softdep, I'd say the performance was at
least four times better, if not more (maybe even twice that).
Have I stumbled across the reason softdep is not enabled by default, or
is there some other logic behind this?
While we're on the topic, does anyone have a nice comparison of ffs or
lfs to reiserfs somewhere? I have found a number of (dated) comparisons
of ffs to ext2.