[Dev-luatex] luafontloader virtual access (bug #404, #448)

Taco Hoekwater taco at elvenkind.com
Wed Sep 8 18:57:18 CEST 2010


Hi,

On 09/08/2010 07:35 AM, Taco Hoekwater wrote:
>
> In punknova.kern, there tend to be 1242 top-level kern array entries,
> each of which has about a little under a hundred keys. That would be
> over 100k worth of metatable lookups, and that will definitely be
> slower than accessing the actual table that is returned at the moment.

Also, each of those metatable calls would introduce a new userdata
object to be garbage collected.

Hans and I just did some tests, and it seems that the userdata access
is useful if *but only if* you are very low on memory. In other cases,
it just adds extra objects to be garbage collected, which makes the
collector slower. That is on top of extra time spent on the actual
calls, and even worse: those extra gc objects tend to be scattered
around in memory, resulting in extra minor page faults (cpu cache
misses) and all that has a  noticeable  effect on run speed: the
metatable-based access is 20-30%  slower than the old massive to_table.

Therefore, there seems little point in expanding the metadata
functionality any further. What is there will stay, but adding more
metadata objects appears to be a waste of time on all sides.

Best wishes,
Taco



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