On 09/24/2018 01:41 PM, Peter Maydell wrote:
> On 19 September 2018 at 11:19, Cédric Le Goater <c...@kaod.org> wrote:
>> These are the number of read operations done on the flash memory region :
>>
>> 922478 ~ 3.5 MBytes OpenBMC U-Boot
>> 20569977 ~ 80 MBytes Mainline U-Boot
>>
>>
>> So we are trashing the TBs I would say. Is there a way to increase the
>> TB size ? or some other TB parameter ? Is that directly linked to the
>> instruction cache size ?
>
> Well, execution direct from MMIO means we read each instruction
> as we execute it -- there's no caching of TBs. (We generate a
> temporary TB with a single insn and throw it away after executing
> from it.) This is because we can't be sure that we would get the
> same data value the next time we read from the address.
In our case, we should have the same data. So may be I can introduce
a read-only region with a cache to speed up the accesses. A bit like
this was done with the previous mmio inteface.
> So we definitely expect things to go slower -- I'm just a little
> surprised that we spend so much time executing from flash devices
> that aren't in "romd" mode.
Yes. it is very slow but some instructions are loaded more than
250.000 times. See below.
Thanks,
C.
count address
... ...
149113 0x28a18
149113 0x28a1c
149113 0x28a20
149113 0x28a24
149113 0x28a28
149113 0x28a2c
149113 0x28a30
149113 0x28a34
149113 0x28a38
149113 0x28a3c
149113 0x28a40
253584 0x288b4
253584 0x288bc
253584 0x288c0
253584 0x288c8
253584 0x288cc
253584 0x288d4
253584 0x288e0
253584 0x288e4
253584 0x288f0
253584 0x288f4
253584 0x288fc
253584 0x28904
253584 0x28908
253584 0x28910
253584 0x28914
253584 0x28920
253584 0x28924
253584 0x28928
253584 0x2892c
253584 0x28934
253584 0x28938
253584 0x2893c
253584 0x28940
253584 0x28944
253584 0x2894c
253584 0x28954
253584 0x28958
253584 0x2895c
253584 0x28960
253584 0x28964
253584 0x28968
253584 0x2896c
253584 0x28970
253584 0x28974
253584 0x28978
253584 0x2897c
253584 0x28980
253584 0x53364
253585 0x288b8
253585 0x288c4
253585 0x288d0
253585 0x288d8
253585 0x288dc
253585 0x288f8
253585 0x28900
253585 0x2890c
253585 0x28918
253585 0x2891c
253585 0x28948
253585 0x53344
253586 0x28930
253586 0x28950
253587 0x288b0
257497 0x53348
277523 0x53354
