From: Stefan Monnier <monnier@IRO.UMontreal.CA>
To: Paul Eggert <eggert@cs.ucla.edu>
Cc: emacs-devel@gnu.org
Subject: Re: Lisp_Marker size on 32bit systems
Date: Fri, 07 Sep 2018 23:10:31 -0400 [thread overview]
Message-ID: <jwvefe4n0tu.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <499c51c7-37c0-0b4f-442c-8f83f1574523@cs.ucla.edu> (Paul Eggert's message of "Fri, 7 Sep 2018 20:04:52 -0700")
>> Those perf-stats also show improved I$ performance, which isn't
>> explained by your suggested explanation. Similarly, they show
>> a reduced number of instructions.
>
> Yes, it could well be that the 32-byte allocation is faster than the 24
> partly due to some reason other than d-cache effects. Although there
> is a smaller percentage of cache misses in the 32-byte version, it could be
> that this is because the 32-byte version uses simpler code that would be
> faster even if the cache miss rate were the same.
That's my impression as well, but I'd be curious to know why that is.
The only "obvious" advantage is that 32 is a power of 2 so you can use
shift for multiplication/division, but that would only apply to things
like indexing arrays of markers or computing the diff between two
marker pointers. AFAIK we don't do any such operation.
Stefan
prev parent reply other threads:[~2018-09-08 3:10 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-06 0:41 Lisp_Marker size on 32bit systems Stefan Monnier
2018-09-06 6:51 ` Paul Eggert
2018-09-06 12:17 ` Stefan Monnier
2018-09-07 7:15 ` Paul Eggert
2018-09-07 8:05 ` Eli Zaretskii
2018-09-07 13:45 ` Paul Eggert
2018-09-07 14:12 ` GDB and compiler-operations (was: Lisp_Marker size on 32bit systems) Stefan Monnier
2018-09-07 14:23 ` Eli Zaretskii
2018-09-07 15:16 ` GDB and compiler-operations Andreas Schwab
2018-09-07 15:48 ` GDB and compiler-operations (was: Lisp_Marker size on 32bit systems) Paul Eggert
2018-09-07 15:58 ` GDB and compiler-operations Stefan Monnier
2018-09-07 17:11 ` Eli Zaretskii
2018-09-07 17:15 ` Paul Eggert
2018-09-07 19:59 ` Tom Tromey
2018-09-07 14:19 ` Lisp_Marker size on 32bit systems Eli Zaretskii
2018-09-07 16:27 ` Paul Eggert
2018-09-07 17:16 ` Eli Zaretskii
2018-09-07 18:13 ` Paul Eggert
2018-09-07 18:32 ` Eli Zaretskii
2018-09-07 19:05 ` Paul Eggert
2018-09-07 19:22 ` Eli Zaretskii
2018-09-07 12:16 ` Stefan Monnier
2018-09-07 19:04 ` Paul Eggert
2018-09-07 19:45 ` Stefan Monnier
2018-09-07 21:03 ` Paul Eggert
2018-09-08 1:54 ` Stefan Monnier
2018-09-08 3:04 ` Paul Eggert
2018-09-08 3:10 ` Stefan Monnier [this message]
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