code runs faster after CPC is disabled (T1040RDB)

[hv]

I have an application that seems to run faster after I disabled CPC.  What's the explanation for that?  Does anyone have any ideas?  I would expect that the code would run slower, not faster.  Thanks!

[alexander_yakov]

Unfortunately, it is difficult to debug this situation "in general", without an information what your "code" is exactly doing and how exactly you are disabling CPC.

In general I think it is possible to imagine a situation, where disabling cache may give some performance benefit, however this is for very specific case. First what comes to mind is write-back vs write-through cache on write operations.

Have a great day,
Alexander

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[hv]

Thanks Alexander! I disabled the CPC by doing these steps based on the T1040RM document since u-boot already enabled CPC:

1. Clear all bits of CPCPARn (this prevents any new transactions from allocating into

the CPC) using write operation.

2. Flush the CPC using one of the two following methods:

• Harware flush: Set CPCCSR0[CPCFL] and wait for hardware to clear

CPCCSR0[CPCFL] by polling

• Software flush: perform a dcbf operation to each coherency granule mapped to

the memory target (that is, one dcbf for each 64 bytes).

3. Clear all lock bits by setting CPCCSR0[CPCLFC].

4. Wait for hardware to clear CPCCSR0[CPCLFC] using a polling loop.

5. Disable the CPC by clearing CPCCSR0[CPCE].

I was baffled because the code in question is pretty cache-intensive! So when it runs faster after L3 is disabled is very confusing! So any help is greatly appreciated!

[alexander_yakov]

Do you agree with my concern that it is really difficult to debug the situation without an information what your "cache-intensive code" is exactly doing?

If you want to continue debugging this situation "in general", than I can suggest checking your platform frequency configuration (CPC is a part of platform) and check your CPC setting before disabling.

[hv]

I agree. I was just hoping that someone on the forum might have some insights or experiences with cases like this.

Thanks!