consistent_alloc changes for 4xx/8xx

Ralph Blach rcblach at
Tue Jan 22 07:45:02 EST 2002

Dan, here are my responces.

>>Another, more challenging, situation also exists because you can't use
>>the __va()/__pa() macros on the addresses returned from consistent_alloc
>>On the 4xx/8xx, the virt_to_* macros will call iopa() which will track
>>the real physical address in the page table, which continues to work.

On the IBM book E part, __va()/__pa() will have to be obsoleted.  The
address space is
36 bits.  Better now than later.

>>For testing, I added the ability on the MPC860 to pin the first 8M of
>>text (of which there is probably on 512K used), up to 24 Mbytes of kernel
>>data, and the 8M IMMR space.  Note that this will only work on the 860
>>processors with a 32 entry TLB.  I added, but couldn't test for lack of
>>hardware, a similar feature to the 4xx.  I wanted to check this in before
>>kernel changed too much, and I have volunteers testing it, so any
>>should be corrected shortly.  Note that this TLB pinning comes at a cost
>>taking TLB entries out of use for applications, so IMHO it isn't
>>that should be done without verification of total system performance
>>I hope someone can find some benchmarks where this feature actually

Dan, you saw netperf which  demonstrated the benefit.  These were the very
test you
suggested we run and they showed a >10% performance increase on a 405.


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