[Mesa-dev] [PATCH] src: replace RTLD_NOW with RTLD_LAZY

[Eric Anholt]

Rob Clark <robdclark at gmail.com> writes:

> On Fri, Aug 5, 2016 at 8:42 PM, Jan Ziak <0xe2.0x9a.0x9b at gmail.com> wrote:
>> Mesa source code prior to this patch uses both RTLD_NOW and RTLD_LAZY.
>> This patch removes all RTLD_NOW in favor of RTLD_LAZY.
>>
>> In comparison to early binding, lazy binding reduces CPU instruction count
>> of small GL apps (e.g: glxinfo) by 6 million instructions.
>> Larger apps won't notice the difference.
>
> tbh, I don't know the background of existing places that use RTLD_LAZY
> instead of RTLD_NOW (but my experience w/ xserver using LAZY has not
> been positive, so I think going the other direction seems like a good
> idea).. But I'm not sure that optimizing for glxinfo is the best goal.
> I know that at least for freedreno a lot of the startup time for small
> real gl apps (ie. something that mostly matters for piglit runs) goes
> to constructing regalloc interference graph..  maybe there is some way
> to leverage what is being done for on-disk shader cache to cache some
> of this up-front work and make a meaningful reduction in startup cost
> for things that actually do a bit more than glxinfo.  (Plus speeding
> up piglit runs is actually a real world benefit..)

I do think that RTLD_LAZY makes sense, and there's no reason to waste
the CPU time if we don't need it.  If nothing else, we all run a lot of
piglit processes that all create contexts.  As far as "what if there are
unresolved symbols or something?", I think if we have symbols not being
covered by piglit even once, we've already lost.

For your regalloc, have you looked at i965's direct q value calculation
in brw_fs_reg_allocate.cpp?  That might save you a ton of time.  That
said, I was skimming a paper recently that seemed to be saying that if
you can assume a not-completely-general set of register classes, you can
do the equivalent of the pq test without the giant table.
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