Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ukma!rutgers!rochester!pt.cs.cmu.edu!andrew.cmu.edu!bader+
From: bader+@andrew.cmu.edu (Miles Bader)
Newsgroups: comp.sys.amiga
Subject: Re: shared/loaded libraries vs. resident
Message-ID: <4YHrsOy00UkaA1YJRE@andrew.cmu.edu>
Date: 21 Apr 89 19:16:42 GMT
References: <13492@louie.udel.EDU>,
	<8635@polya.Stanford.EDU>
Organization: Information Technology Center, Carnegie Mellon, Pittsburgh, PA
Lines: 23
In-Reply-To: <8635@polya.Stanford.EDU>

gilham@polya.Stanford.EDU (Fred Gilham) writes:
> The thing that concerns me about this is the performance hit.  I read
> somewhere that the cost of a library call is about 100us.  You really
> can't do anything about this, either; no optimization possible.  The
> cost of a procedure call should be smaller (right?).

I thought that a "library" call involved only the extra overhead of the jmp
instruction in the library entry vector, which is 12 cycles on a 68000.

Your JSR also has to be relative to the library pointer, but this is CHEAPER
than an absolute one.  You also have the overhead of moving the pointer into
register a6 (?), which is typically 16 cycles if needed-- the compiler should
be keeping it there across multiple calls.

So, as far as I can see, there's a max of around 28 extra cycles or about 4us
on the amiga.

You may be thinking of the extra overhead of a stub to move the arguments
into registers when calling from a c program, but this isn't really
necessary, as the lattice #pragma for making direct library calls
illustrates.

-Miles