Re: [linuxsh-dev] cache handling

[SUGIOKA T. <su...@it...>]

At 14:48 02/04/25 +0900, SUGIOKA Toshinobu <su...@it...> wrote:
>At 10:44 02/04/25 +0900, NIIBE Yutaka <gn...@m1...> wrote:
>> > (2) For flushing O-cache entry, we can use movca.l/ocbi pair while BL 
>>bit is set.
>> >     This sequence can be executed in P1 area and does not cause any 
>>unnecessary bus cycles.
>>
>>I don't know well about this.  Why/How those are different with ocbp?
>>Do you have any reference?
>
>The data written by "movca.l r0,@rn" here is just a garbage, so it should not be
>written back to real memory. "ocbi" is better because it does not cause 
>write back
>cycle, and no extra address space is needed for writing garbage data.
>I used 16kB aligned block which include empty_zero_page for this purpose. 
>If garbage were
>written into this area, kernel would crash immediately :P.

Possibly I misunderstood your question.
We can't use ocbp instead of movca.l/ocbi for flush cache all. 'ocbp' flushes only when
the tag of the cache-line is matched to the specified address.
On the other hand, movca.l/ocbi flushes specified cache-line unconditionally.

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SUGIOKA Toshinobu