Dropping CONFIG_REORDER on x86-64 for 2.6.22

[Andi Kleen]

Hallo,

I'm thinking about dropping the x86-64 CONFIG_REORDER for 2.6.22. 
The function enabled -ffunction-sections and then tries to reorder
the executable

While that's in theory a worthy goal to save TLB/icache, in practice it 
didn't really work out.

Rationale:
- It cannot be enabled in normal builds because all current lds
become very slow when they have to handle thousands of sections.

- The list of hot functions it needs - arch/x86_64/kernel/functionlist -
hasn't been changed for a long time and is already out of date. 
I also don't know no sane way to keep it uptodate. Profile feedback
at runtime is not practical for the kernel and even if it's questionable
we would find a good training workload. Trying to change the manually
is imho foolish and likely not too useful anyways (if any hot function
is missed the TLB savings will be lost and it is unlikely we can
get 100% coverage) 

- The workloads of the kernel are too diverse to make this concept
really work

So I'm planning to drop the option and arch/x86_64/kernel/functionlist

Comments?

-Andi

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/