possible regression?

[Greg Freemyer]

On Mon, Jan 24, 2011 at 7:28 AM, Mag Gam <magawake at gmail.com> wrote:
> This is just for curiosity.  I think its strange this is occurring
> that's all. It did not happen in the older kernels but its happening on
> the newer versions. Possibly there maybe more like this.

< snip of everything below the top post ;)   For the future,  we
bottom post exclusively here. >

I was not trying to shoot down your question, just find out if your
were seeing a real world problem or not.

The dd performance test you ran is basically artificial, so even if
you track down why it slowed down, it could easily be that it is
related to a functional improvement that the kernel team will consider
much more important than an artificial performance test.

A even more frustrating example is around 2.6.32 I think, the mdraid
layer of the kernel got barrier support.  Lot's of real world apps saw
their performance drop significantly.

But it was only because not having barriers is a lot faster than
having them, but it is also inherently much more dangerous.  And there
is a mount option to disable barrier support.  So users that
complained were told it was their option.  Either be safe and accept
the new slow performance, or be risky and start using the nobarriers
mount option.

Only after track down the source of performance drop will you be able
to have that discussion.  Good luck hunting.

fyi: How to perform that hunt is a very appropriate discussion for
this list, but you might want to change the subject to reflect it if
that's what you want to discuss next.

Good Luck
Greg