Le 14/10/2016 à 12:03, Jean-Yves Migeon a écrit :
I would benchmark both (with and without the "overhead" introduced); a
while back when implementing PAE I did not expect the paddr_t promotion
from 32 to 64 bits to have that much of an impact on pmap performance,
but the first attempt induced more that 5% overhead on a "cold"
./build.sh run.

Granted, you are not dealing with the same situation here but pool
caches make the allocation used/unused dance almost free (except for the
slow path). When objets are in the pool cache but not yet obtained
through the getter, they are still allocated but basically not used. It
would be interesting to see if the hit/miss ratio is affected for the
"pvpl" pool with your optimization.

I tried to, but the only netbsd machine I have access to now is a vm. The
result I got was that I saved roughly one minute of compilation on a clean
'./build.sh tools'. But obviously, the performance in this case depends a
lot on what resources the host decides to grant, so I guess the uncertainty
is too big for this one minute to be significant.

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