Re: [RFC 1/6] Framework

[Nick Piggin <nickpiggin@yahoo.com.au>]

Andi Kleen wrote:

>>Then you can't use __local_xxx, and so many architectures will use
>>atomic instructions (the ones who don't are the ones with tripled
>>cacheline footprint of this structure).
> 
> 
> They are wrong then. atomic instructions is the wrong implementation
> and they would be better off with asm-generic. 
> 

Yes I mean atomic and per-cpu. Same as asm-generic.

> If anything they should use per_cpu counters for interrupts and 
> use seq locks.

How would seqlocks help?

> Or just turn off the interrupts for a short time
> in the low level code.
> 

This is exactly what mod_page_state does, which is what my patches
eliminate. For a small but significant performance improvement.

> 
>>Sure i386 and x86-64 are happy, but this would probably slow down
>>most other architectures.
> 
> 
> I think it is better to fix the other architectures then - if they
> are really using a full scale bus lock for this they're just wrong.
> 
> I don't think it is a good idea to do a large change in generic
> code just for dumb low level code.
> 

It is not a large change at all, just some shuffling of mod_page_state
and friends to go under pre-existing interrupts-off sections.

-- 
SUSE Labs, Novell Inc.

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