Hi Andrew,
On Fri, Jul 31, 2015 at 8:30 PM, Andrew Bradford andrew@bradfordembedded.com wrote:
Hi Bin,
On 07/30 12:12, Bin Meng wrote:
Hi Simon,
When adding x86 multi-cpu initialization on a board with 4 cores, I found:
=> cpu list 0: cpu@0 Genuine Intel(R) CPU @ 1.58GHz 1: cpu@1 Genuine Intel(R) CPU @ 1.58GHz 2: cpu@2 Genuine Intel(R) CPU @ 1.58GHz 2: cpu@3 Genuine Intel(R) CPU @ 1.58GHz
cpu@2 and cpu@3 have the same sequence number, which indicates they are running parallelly to get the same sequence number. The call chain on an ap is: mp_init_cpu() -> device_probe() -> uclass_resolve_seq(). Apparently ap2 and ap3 are running at the same time to get the same number.
Note so far all x86 boards that we have enabled x86 multi-cpu initialization on only have 2 cores, which will not expose such issue as there is no parallel execution among aps.
What does this mean?
- Driver model is not smp safe. But given U-Boot is a single-threaded
environment, I don't think we want to add such support to driver model.
OR:
- We are using driver model incorrectly on x86 mp initialization codes.
What do you think?
I'm not sure what to do about this (if anything) but I also see this on an E3845 based board. I don't think it has affected me in any way.
So far I only see the seq number is not correct. Booting Linux with MP table seems to be OK as Linux can start all 4 cores correctly.
Does this also affect non-x86 processors?
I believe currently the cpu uclass is only implemented on x86, so only x86 is affected for now.
=> cpu list 0: cpu@0 Intel(R) Atom(TM) CPU E3845 @ 1.91GHz 2: cpu@1 Intel(R) Atom(TM) CPU E3845 @ 1.91GHz 2: cpu@2 Intel(R) Atom(TM) CPU E3845 @ 1.91GHz 1: cpu@3 Intel(R) Atom(TM) CPU E3845 @ 1.91GHz
Regards, Bin