Re: the P2M/VP patch merge plan (was Re: [Xen-ia64-devel] [PATCH][RFC][TAKE5] the P2M/VP patches)

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

On Wed, May 17, 2006 at 04:15:38PM +0200, Tristan Gingold wrote:

> I'd just like to understand clearly why and where locks must be added.
> Adding locks has a cost and must be understood in order to be done correctly.

Yes lock has a cost.
If lockless approache was achieved, it would be a big win especially
on a big iron.
However are you really sure about all races?
If there are a bug, it must rarely happen and be very nasty.
It would be almost impossible to debug such a bug.
Instead, a certain way should be adopted at first although
its performance may be poor.
Once stablilized, we should do performance tuning.
Lockless aproach should be a one of the tuning candidates.

I don't think lockless approach should be taken at the early stage,
especially when perfomance optimization is planned.
Since lockless code is very difficult to modify, trying another 
tuning idea becames very diffucalt.

Thanks.
-- 
yamahata

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