Re: Patch to reorder functions in the vmlinux to a defined order

[Arjan van de Ven <arjan@linux.intel.com>]

Zwane Mwaikambo wrote:
> On Thu, 23 Feb 2006, Arjan van de Ven wrote:
> 
>> This patch puts the infrastructure in place to allow for a reordering of
>> functions based inside the vmlinux. The general idea is that it is possible
>> to put all "common" functions into the first 2Mb of the code, so that they
>> are covered by one TLB entry. This as opposed to the current situation where
>> a typical vmlinux covers about 3.5Mb (on x86-64) and thus 2 TLB entries.
>> (This patch depends on the previous patch to pin head.S as first in the order)
> 
> Hello Arjan,
> 	Assuming that functions defined in an object file are related and 
> hence benefit from cache spatial locality, doesn't this affect this 
> greatly? It would seem that with regards to the kernel image on x86, (2MB) 
> TLB usage isn't as scarce a resource as icache.

this is probably a mixed blessing; right now frequent and non-frequent 
code are highly intermixed, so even in the current situation the icache 
isn't optimally used.

So what you sort of want is a thing better than pure "sort", a sort that 
keeps existing order *within the hot functions*, but move the "cold" 
ones out. That is thankfully independent of the infrastructure; I'll 
keep that in mind when making the next version of the order list, it's a 
good idea.