From: George Spelvin <lkml@sdf.org>
To: linux-kernel@vger.kernel.org, linux@rasmusvillemoes.dk, lkml@sdf.org
Cc: akpm@linux-foundation.org, andriy.shevchenko@linux.intel.com,
daniel.wagner@siemens.com, dchinner@redhat.com,
don.mullis@gmail.com, geert@linux-m68k.org, st5pub@yandex.ru
Subject: Re: [PATCH 4/5] lib/list_sort: Simplify and remove MAX_LIST_LENGTH_BITS
Date: Sun, 10 Mar 2019 22:29:24 GMT [thread overview]
Message-ID: <201903102229.x2AMTOoU009609@sdf.org> (raw)
In-Reply-To: <3194949c-6e04-da01-68df-60ae344db099@rasmusvillemoes.dk>
Rasmus Villemoes wrote:
> On 05/03/2019 04.06, George Spelvin wrote:
>> + * (Actually, it is always called with @a being the element which was
>> + * originally first, so it is not necessary to to distinguish the @a < @b
>> + * and @a == @b cases; the return value may be a simple boolean. But if
>> + * you ever *use* this freedom, be sure to update this comment to document
>> + * that code now depends on preserving this property!)
>
> This was and still is used at least by the block layer, and likely
> others as well. While 3110fc79606fb introduced a bunch of if() return -1
> else if () ... stuff, it still ends with a 0/1 result. Before
> 3110fc79606fb, it was even more obvious that this property was used.
Ah, thank you! I actually read through every list_sort caller in
the kernel to see if I could find anywhere that used it and couldn't,
but I didn't study this code carefully enough to see that it does
in the last step.
Since someone *does* use this, I'll change the comment signiicantly.
> Grepping around shows that this could probably be used in more places,
> gaining a cycle or two per cmp callback, e.g. xfs_buf_cmp. But that's of
> course outside the scope of this series.
The one that misled me at first was _xfs_buf_obj_cmp, which returns 0/1,
but that's not used by list_sort(). xfs_buf_cmp returns -1/0/+1.
As you might see from the comment around the cmp_func typedef,
there are other things that could be cleaned up if we did a pass
over all the call sites.
(I'm almost tempted to tell the compiler than cmp_func is const,
since it's supposed to be independent of the pointer frobbing that
list_sort does, but then I remember Henry Spencer's maxim about
lying to the compiler.)
next prev parent reply other threads:[~2019-03-10 22:30 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-09 2:17 [PATCH 0/5] lib/sort & lib/list_sort: faster and smaller George Spelvin
2019-02-21 6:30 ` [PATCH 1/5] lib/sort: Make swap functions more generic George Spelvin
[not found] ` <20190309140653.GO9224@smile.fi.intel.com>
2019-03-09 15:53 ` lkml
2019-03-09 20:19 ` Andrey Abramov
2019-03-14 9:29 ` Andy Shevchenko
2019-03-14 10:09 ` George Spelvin
2019-03-14 10:41 ` Geert Uytterhoeven
2019-03-14 11:53 ` George Spelvin
2019-03-14 12:18 ` Andy Shevchenko
2019-03-14 19:59 ` Andrey Abramov
2019-03-15 3:35 ` George Spelvin
2019-03-15 8:27 ` Geert Uytterhoeven
2019-03-14 10:11 ` George Spelvin
2019-03-09 21:02 ` George Spelvin
2019-03-13 21:23 ` Rasmus Villemoes
2019-03-13 22:02 ` Geert Uytterhoeven
2019-03-13 23:15 ` George Spelvin
2019-02-21 8:21 ` [PATCH 2/5] lib/sort: Use more efficient bottom-up heapsort variant George Spelvin
2019-03-13 22:29 ` Rasmus Villemoes
2019-03-14 0:03 ` George Spelvin
2019-03-14 0:15 ` Rasmus Villemoes
2019-02-21 8:21 ` [PATCH 3/5] lib/sort: Avoid indirect calls to built-in swap George Spelvin
2019-03-05 3:06 ` [PATCH 4/5] lib/list_sort: Simplify and remove MAX_LIST_LENGTH_BITS George Spelvin
2019-03-10 21:54 ` Rasmus Villemoes
2019-03-10 22:29 ` George Spelvin [this message]
2019-03-14 9:10 ` Andy Shevchenko
2019-03-14 9:41 ` George Spelvin
2019-03-15 4:33 ` George Spelvin
2019-03-15 8:20 ` Geert Uytterhoeven
2019-03-15 10:23 ` George Spelvin
2019-03-15 12:57 ` Geert Uytterhoeven
2019-03-15 16:59 ` George Spelvin
2019-03-15 17:47 ` Geert Uytterhoeven
2019-03-15 18:53 ` Andrey Abramov
2019-03-15 19:06 ` Andy Shevchenko
2019-03-15 19:23 ` Andrey Abramov
2019-03-15 19:56 ` Andy Shevchenko
2019-03-16 3:49 ` George Spelvin
2019-03-05 5:58 ` [PATCH 5/5] lib/list_sort: Optimize number of calls to comparison function George Spelvin
2019-03-13 23:28 ` Rasmus Villemoes
2019-03-14 1:58 ` George Spelvin
2019-06-21 23:12 ` Rasmus Villemoes
2019-12-08 8:01 ` George Spelvin
2019-03-15 19:54 ` [PATCH 0/5] lib/sort & lib/list_sort: faster and smaller Andrey Abramov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=201903102229.x2AMTOoU009609@sdf.org \
--to=lkml@sdf.org \
--cc=akpm@linux-foundation.org \
--cc=andriy.shevchenko@linux.intel.com \
--cc=daniel.wagner@siemens.com \
--cc=dchinner@redhat.com \
--cc=don.mullis@gmail.com \
--cc=geert@linux-m68k.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@rasmusvillemoes.dk \
--cc=st5pub@yandex.ru \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).