Re: [PATCH 00/23] per device dirty throttling -v8

Andrew Morton
2007-08-05T20:40:47Z

On Sun, 5 Aug 2007 22:21:12 +0200 Jörn Engel <joern@logfs.org> wrote:

> On Sun, 5 August 2007 20:37:14 +0200, Jörn Engel wrote:
> >
> > Guess I should throw in a kernel compile test as well, just to get a
> > feel for the performance.
>
> Three runs each of noatime, relatime and atime, both with cold caches
> and with warm caches. Scripts below. Run on a Thinkpad T40, 1.5GHz,
> 2GiB RAM, 60GB 2.5" IDE disk, ext3.
>
> Biggest difference between atime and noatime (median run, cold cache) is
> ~2.3%, nowhere near the numbers claimed by Ingo. Ingo, how did you
> measure 10% and more?

Ingo had CONFIG_DEBUG_INFO=y, which generates heaps more writeout,
but no additional atime updates.

Ingo had a faster computer ;) That will generate many more MB/sec
write traffic, so the cost of those atime seeks becomes proportionally
higher. Basically: you're CPU-limited, Ingo is seek-limited.