[PATCH v2 1/5] [ppc] Process dynamic relocations for kernel
suzuki at in.ibm.com
Tue Nov 8 18:11:36 EST 2011
On 11/07/11 20:43, Josh Poimboeuf wrote:
> On Fri, 2011-11-04 at 14:06 +0530, Suzuki Poulose wrote:
>> On 11/03/11 05:06, Josh Poimboeuf wrote:
>>> On Tue, 2011-10-25 at 17:23 +0530, Suzuki K. Poulose wrote:
>>> @@ -137,6 +137,9 @@ get_type:
>>> lwz r0, 8(r9) /* r_addend */
>>> add r0, r0, r3 /* final addend */
>>> stwx r0, r4, r7 /* memory[r4+r7]) = (u32)r0 */
>>> + dcbst r4,r7 /* flush dcache line to memory */
>>> + sync /* wait for flush to complete */
>>> + icbi r4,r7 /* invalidate icache line */
>> Doing it this way has two drawbacks :
>> 1) Placing it here in relocate would do the flushing for each and every update.
> I agree. My kernel had around 80,000 relocations, which means 80,000
> d-cache line flushes (for a 32k d-cache) and 80,000 i-cache line
> invalidates (for a 32k i-cache). Which is obviously a little overkill.
> Although I didn't notice a performance hit during boot.
>> 2) I would like to keep this code as generic as possible for the PPC32 code.
>> Could we move this to the place from relocate is called and flush the d-cache and
>> i-cache entirely ?
> Why not put the cache flushing code at the end of relocate? Would some
> of the other PPC32 platforms not require the cache flushing?
What I was suggesting is, instead of flushing the cache in relocate(), lets do it
for e.g, on 440x, (in head_44x.S :)
#Flush the d-cache and invalidate the i-cache here
This would let the different platforms do the the cache invalidation in their
Btw, I didn't find an instruction to flush the entire d-cache in PPC440 manual.
We have instructions to flush only a block corresponding to an address.
However, we have 'iccci' which would invalidate the entire i-cache which, which
I think is better than 80,000 i-cache invalidates.
Kumar / Josh,
Do you have any suggestions here ?
> My PPC32 knowledge is 4xx-centric, so please feel free to rewrite the
> patch as needed to accommodate other PPC32 cores.
Same here :)
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