possible regression?

Mag Gam magawake at gmail.com
Tue Jan 25 07:55:12 EST 2011

I appreciated the reply Greg! and thanks for the encouragement.

On Mon, Jan 24, 2011 at 2:23 PM, Greg Freemyer <greg.freemyer at gmail.com> wrote:
> 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

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