F8/9 6-16x slower than XP to boot

[Dave Jones]

On Sat, Mar 29, 2008 at 06:49:53AM -0400, Alan Cox wrote:
 > On Sat, Mar 29, 2008 at 10:08:37AM +0100, Martin Sourada wrote:
 > > Yeah, I agree, but after going trough the article I cannot pass by in
 > > silence the fact that while in Fedora 5 the disk maximum throughput was
 > > 29 MB/s in Rawhide it's only 8 MB/s which is nearly 4x less...
 > 
 > That would be a bug or a misconfiguration somewhere. I'm suprised someone
 > would put that in an article instead of filing a bug.

The idea of using bootchart to measure disk performance seems a bit suspect.
For example, FC5 had the readahead service enabled, so the disk got to do a
serialised burst of reading of a few hundred MB of data.   Now that we don't have
that service, the disk isn't being used as much, so we never see those sorts of peaks,
leading to more 'spiky' bursts of IO in the graph than large blocks.

Treating this as a "how fast disk throughput is" is bogus. It's "what was the
largest amount of data we read in one second".   Given the access patterns
are completely different between releases, comparisons of this number are
completely meaningless.

Something else also stands out, comparing the graphs.
The peaks in all the earlier "high score" results are during either
the readahead service, or rhgb (earlier versions of X did tons of disk IO
doing dumb things like loading modules it didn't need).


None of this excuses why bootup performance still sucks in F9, but
"the disk got slower" isn't the reason.  Or at least it shouldn't be.
I'd rather see results from a real disk benchmark confirming this than
the hand-waving done by the phoronix guys misinterpreting what bootchart is saying.

	Dave

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