From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: George Spelvin <lkml@sdf.org>, linux-kernel@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
Andrey Abramov <st5pub@yandex.ru>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Daniel Wagner <daniel.wagner@siemens.com>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Don Mullis <don.mullis@gmail.com>,
Dave Chinner <dchinner@redhat.com>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Subject: Re: [PATCH 4/5] lib/list_sort: Simplify and remove MAX_LIST_LENGTH_BITS
Date: Sun, 10 Mar 2019 22:54:41 +0100 [thread overview]
Message-ID: <3194949c-6e04-da01-68df-60ae344db099@rasmusvillemoes.dk> (raw)
In-Reply-To: <dd447448384883bd42c41f0de6a83430b6435dc1.1552097842.git.lkml@sdf.org>
On 05/03/2019 04.06, George Spelvin wrote:
> * The comparison function @cmp must return a negative value if @a
> * should sort before @b, and a positive value if @a should sort after
> * @b. If @a and @b are equivalent, and their original relative
> * ordering is to be preserved, @cmp must return 0.
> + *
> + * (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. So
I agree that it is worth documenting this feature, both for users of
list_sort, but even more so for future refactorers of it - but you
probably want to change the wording somewhat.
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.
Rasmus
next prev parent reply other threads:[~2019-03-10 21:54 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 [this message]
2019-03-10 22:29 ` George Spelvin
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
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