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From: Stefan Monnier <monnier@iro.umontreal.ca>
To: Ken Raeburn <raeburn@raeburn.org>
Cc: emacs-devel@gnu.org
Subject: Re: GC: cons sweeping and cons block size
Date: Fri, 06 Jul 2007 08:48:05 -0400	[thread overview]
Message-ID: <jwvzm293dnh.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <E83F4FB7-DF31-4E17-BAB2-E4F2148E024E@raeburn.org> (Ken Raeburn's message of "Fri\, 6 Jul 2007 07\:54\:46 -0400")

> (quoting David, who was quoting Stefan)
>>>> I haven't found the time to do it, but it would be good to get  rid of
>>>> this situation and always place tags in the 3 LSB bits.

> It does appear to be the default for most systems, maybe all modern ones,
> but only when we compile with GCC.  Are we confident no one is using Emacs
> on systems where we use a system malloc that doesn't do 8-
> byte alignment?

No.  IIRC at least Mac OS 9's malloc doesn't do 8-byte alignment.
By getting rid of the MSB tags I meant write the code to handle the case
where malloc doesn't return multiples of 8 and where we can't use GCC's
alignment attribute to force alignment on static (and/or stack structures).

> We could do a USE_LSB_TAG variant of the union, to get more address  space
> back but keep the paranoid type checking capability.

If we can really get the exact same performance, maybe it's a good idea, but
since it's only really useful at compile-time, it's quite sufficient to
compile the source every once in a while with the USE_LISP_UNION_TYPE flag.


        Stefan

  reply	other threads:[~2007-07-06 12:48 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-07-04  6:43 GC: cons sweeping and cons block size dmantipov
2007-07-05 14:06 ` Stefan Monnier
2007-07-05 14:42   ` David Kastrup
2007-07-05 16:02     ` Stefan Monnier
2007-07-06 11:54       ` Ken Raeburn
2007-07-06 12:48         ` Stefan Monnier [this message]
     [not found] <E1I5ktS-0001uQ-Uc@monty-python.gnu.org>
2007-07-03 20:22 ` Jonathan Yavner
2007-07-05  1:29   ` Richard Stallman
  -- strict thread matches above, loose matches on Subject: below --
2007-07-03 15:16 Dmitry Antipov

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