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From Otheus <oth...@gmail.com>
Subject [users@httpd] configure bug? concerning use of nonportable atomics
Date Wed, 14 Jan 2009 14:23:52 GMT
Greetings,

A user on unix.com posted this query :

> Does anyone know or know how to check if the Apache 2.2 version you can get with the
Synaptic Package manager in Ubuntu 8.10has been optimized for 486 or higher processors?

He then quotes from the documentation on tuning:
> By default, APR uses mutex-based atomics on Linux. If you configure with --enable-nonportable-atomics,
however, APR generates code that uses a 486 opcode for fast hardware compare-and-swap. This
will result in more efficient atomic operations, but the resulting executable will run only
on 486 and later chips (and not on 386).

 Looking into this, I discovered that the APR's configure code will
use generic atomics (as opposed to inline assembly) under all x86
platforms *except* i386 and x86_64 (and unless specifically overridden
on the command line). Here's the thread in the mailing list which
includes the patch and commentary (but not rationale) from
jorton@apache.org in 2004:
    http://mail-archives.apache.org/mod_mbox/apr-commits/200401.mbox/<20040106150746.91496.qmail@minotaur.apache.org>

My question is: *why* ?? Why default to generic atomics on i486's and
later, but not x86_64? I think this is a bug in the configure logic,
but I'm not sure.


-- 
Otheus
otheus@gmail.com
+43.699.1049.7813

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