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From: "Li,Rongqing" <lirongqing@baidu.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Michel Lespinasse <michel@lespinasse.org>,
	"dbueso@suse.de" <dbueso@suse.de>,
	"mingo@kernel.org" <mingo@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: 答复: 答复: 答复: [PATCH] rbtree: stop iteration early in rb_find_first
Date: Thu, 26 Aug 2021 05:03:54 +0000	[thread overview]
Message-ID: <770bfd98d67e4c6cbfbb341d70ecf448@baidu.com> (raw)
In-Reply-To: <20210825192056.GF17784@worktop.programming.kicks-ass.net>

> You're right that rb_add() does a tail-add for elements it considers equal -- there
> is actually code in the tree that relies on this.
> 
> But that doesn't mean rb_find_first() should go right, it *must*not*, because
> then it wouldn't find the 'first' aka 'leftmost' instance of the equal elements.
> 
> Also, you're only considering building the tree in-order with rb_add(), trees get
> modified all the time and the pattern Michel gave is perfectly valid (also see
> rb_prev()).
> 
> Sure the snippet is not a balanced tree, but you can construct the pattern as
> part of a larger tree just fine, just add some elements:
> 
> 
> 	 10(b)
> 	/  \
>        5   10(c)
>         \
> 	10(a)
> 
> is a tree that is balanced (remember, RB trees only require the left and right
> depths to no more than double -- as opposed to AVL trees, which have a tighter
> constraint). This tree has order: 5, 10(a), 10(b), 10(c).
> Also note that the tree rotations are stable -- they must be since they do not
> refence the order function.
> 
> As such, if we rb_find_first() for 10, we must find 10(a), the leftmost
> 10 in the tree.

I see, Thanks for the explanation. Sorry for the noise.

-Li

  reply	other threads:[~2021-08-26  5:04 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-25  9:59 Li RongQing
2021-08-25 11:39 ` Peter Zijlstra
2021-08-25 11:53   ` Michel Lespinasse
2021-08-25 11:58     ` Michel Lespinasse
2021-08-25 12:31       ` Peter Zijlstra
2021-08-25 13:21       ` Peter Zijlstra
2021-08-25 16:08         ` 答复: " Li,Rongqing
     [not found]         ` <90ea3457ddc7485fbc8db5f7ca5b07ab@baidu.com>
2021-08-25 17:18           ` Peter Zijlstra
2021-08-25 18:26             ` 答复: " Li,Rongqing
2021-08-25 19:20               ` Peter Zijlstra
2021-08-26  5:03                 ` Li,Rongqing [this message]
2021-08-25 12:29     ` Peter Zijlstra
2021-08-25 12:32       ` Peter Zijlstra

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