[Bug 6259] Improve SMP kernel performance on UP systems

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Ubuntu (livecd) | linux


ben.collins at ubuntu.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|SMP support for the live CD |Improve SMP kernel
                   |                            |performance on UP systems




------- Additional Comments From ben.collins at ubuntu.com  2005-09-06 20:03 UTC -------
I did some searching and found that an SMP kernel on a UP system has unavoidable
performance issues due to the nature of the lock operation. Some reports say
that the operation can take as many as 12 cycles from the CPU, and that almost
always it will cause a pipeline flush because of the operation ordering.

However, I did find the below thread and patch, which can be easily ported to
the current kernel:

http://www.ussg.iu.edu/hypermail/linux/kernel/0203.2/0178.html

It implements a function which is called when an SMP kernel boots on a UP
system. In this case, it does a dynamic code rewrite based on a lookup table,
which turns all lock op's into nop's. This is a vast improvement on the standard
SMP kernel when run on a UP system (likely this would also take affect if
someone boots with nosmp).

I suggest for now that we forget about doing anything related to this in breezy.
Post-breezy, it would be nice to start testing this. It should be easy to
implement the same thing for other architectures (ppc, and amd64 for example).

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