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Re: zero filling pages

Shawn Erickson <email@hidden>

I would also suggest that folks consider using Shark which is part of Apple's CHUD tools. It should allow you to sample what is going on, including in the kernel. Why guess when you can sample to see what is causing your delay.

Well no problem. I ran the test and... big surprise! (http://www.vfl4u.de/wbb2/images/smilies/smile40.gif)

For you :) - Most of the time is spent zero filling the pages. In a loop that vm_allocates big amounts of memory, touches all pages and releases them more than 80% of the time is used up by zero filling (on my 450 Mhz Cube with 10.2.6).

Actually the time expended because of zero filling is more than Shark will tell you, because the zero fill routine (as I wrote before) not only wastes the 4K of data cache but also 4K of instruction cache. That slowdown, because of the need to recache, won't show up in Shark in the page zero routine, but instead it will be spread over the following instructions.

Ciao
Nat!

P.S. The actual page zero routine is xnu/osfmk/ppc/movc.s and my impression is that there is a lot of Voodoo in it.
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 >Re: zero filling pages (From: Nat! <email@hidden>)



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