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Re: 604e's suck (was Yaboot Config Question)

On Sat, Apr 07, 2001 at 04:26:02AM -0700, Andrew Sharp wrote:
> I'm afraid it's even worse than that.  I haven't looked up the
> design specs on the web or anything, but I believe the Daystar
> design is quite poor in a number of ways, some of them not really in
> their control.  First, it's not SMP, it's really AMP, or Asymetric
> MP: only processor 0 gets interrupts.  The processor affinity
> algorithms in the 2.2 kernel, lame as they are, cause poor
> performance on this kind of MP architecture.  I wouldn't be
> surprised if 2.0 kernels, which had almost no processor affinity
> code, would show better scaling on these systems.  Secondly, only
> one processor at a time may use the bus off the daughter card, and
> are multiplexed by bus transaction, not by bus cycle.  L2 cache
> thrashing is a definite possibility.  
 Now that I think about it again, maybe the problem is just that the L2
cache is on the mobo, as well as being shared, so the CPUs have to go
through the bottleneck bus to get to it.

> But the worst part is that the
> 604e is but a very pale shadow of the 604, with it's half wide data
> and address busses and basically non-existent L1 caches.  It's
> specmark numbers for a 200 are below those of a 200MHz PentiumPro. 
> So, yes, your 650 Athlon, what with 133 or 200MHz memory bandwidth,
> would spank that snot out of a 4 way 604e @ 150MHz.
> With almost no disk accesses, my dual 200MHz 604e compiles a certain
> kernel config achieving only about a 50% scaling, which is down
> right pitiful, but better than nothing!  My dual SparcStation20 and
> my dual celeron system achieve greater than 95% scaling on the same
> kind of [fairly silly] test.  Such is life.

 It's hardly "fairly silly".  Compiling is an important benchmark, since a
lot of time will be spent actually compiling.

 Thanks for that info.  BTW, only 2.4 kernels support my quad Daystar (2.2
handled dual CPU daystars).  Also, the older Daystar Digital Genesis MP (not
MP+), like I have, uses 604 CPUs, not 604e.  I looked up some info on 604
and 604e before I bought the system (second hand last summer), and IIRC 604e
has better out-of-order execution and stuff like that.  I guess that just
makes the memory starvation worse, though!  I've got two 64MB DIMMs in the
right slots for interleaving to work, but that doesn't help the memory
latency.  I think they still have less bandwidth than the 66MHz SDRAM in my
P200MMX.  (I ran some lmbench tests.)  How much would a CPU upgrade card
help?  Anyone tried compiling a kernel or something with e.g. a dual G4 CPU
card in an old system with interleaved memory?  G3 and G4 cpus have
per-processor cache, instead of the shared 512kB my system has, so they
should do a lot better.

processor       : 0
cpu             : 604
clock           : 150MHz
revision        : 3.5
bogomips        : 299.50

proc 1,2, and 3 identical

total bogomips  : 1196.53
zero pages      : total: 0 (0Kb) current: 0 (0Kb) hits: 0/0 (0%)
machine         : Power Macintosh
motherboard     : AAPL,9500 MacRISC
L2 cache        : 512K unified
memory          : 128MB
pmac-generation : OldWorld

#define X(x,y) x##y
Peter Cordes ;  e-mail: X(peter@llama.nslug. , ns.ca)

"The gods confound the man who first found out how to distinguish the hours!
 Confound him, too, who in this place set up a sundial, to cut and hack
 my day so wretchedly into small pieces!" -- Plautus, 200 BCE

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