Re: 7.52 second kernel compile

[Paul Mackerras]

Linus Torvalds writes:

> Btw, here's a program that does a simple histogram of TLB miss cost, and
> shows the interesting pattern on intel I was talking about: every 8th miss
> is most costly, apparently because Intel pre-fetches 8 TLB entries at a
> time.

Here are the results on my 500Mhz G4 laptop:

   1.85: 22
  17.86: 26
  14.41: 28
  16.88: 42
  34.03: 46
   9.61: 48
   2.07: 88
   1.04: 90

The numbers are fairly repeatable except that the last two tend to
wobble around a little.  These are numbers of cycles obtained using
one of the performance monitor counters set to count every cycle.
The average is 40.6 cycles.

This was with a 512kB MMU hash table, which translates to 8192 hash
buckets each holding 8 ptes.  The machine has 1MB of L2 cache.

Paul.