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From: Chuck Lever <cel@citi.umich.edu>
To: Linus Torvalds <torvalds@osdl.org>
Cc: Junio C Hamano <junkio@cox.net>, git@vger.kernel.org
Subject: Re: [PATCH 0/2] A new merge algorithm, take 3
Date: Thu, 08 Sep 2005 14:16:06 -0400	[thread overview]
Message-ID: <43207FE6.2030108@citi.umich.edu> (raw)
In-Reply-To: <Pine.LNX.4.58.0509081012540.3208@g5.osdl.org>

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Linus Torvalds wrote:
> 
> On Thu, 8 Sep 2005, Junio C Hamano wrote:
> 
>>Yes, the reading of three trees upfront is probably the culprit
>>in your case
> 
> 
> However, note that _most_ tree reading just reads one.
> 
> Merges may take half a second, and yes, when I did it, the fact that we 
> move things around in the array is by far the highest cost. But the thing 
> is, if merges take half a second, that's still not only damn good, it's 
> not even the most common operation.

in my case the merges were taking significantly longer than a half 
second.  making this change is certainly not worth it if merges are 
running fast...

> Yes, the active_cache[] layout as one big array is inconvenient for 
> read_tree(), which tends to want to interleave different trees in the 
> array and thus forces things to be moved around.
> 
> But remember what the most common use for the index is - it's the "single 
> tree" case from read_cache(). That's _so_ much more common than 
> read_tree() that it's not even funny.

read_cache is fast as implemented.  the issue is that the next thing 
that is often done is a cache insert, which requires a memmove, which is 
slow.

> So the data structure is optimized for a different case than reading in 
> trees. Big deal. That optimization is definitely worth it: it allows us to 
> do the read_cache() with the actual index entries being totally read-only 
> (a linked list would have to add a "next" pointer to the cache entries and 
> not allow the in-place thing that read_cache() does).

they are still read-only with my linked list implementation.

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  parent reply	other threads:[~2005-09-08 18:16 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-09-07 16:47 [PATCH 0/2] A new merge algorithm, take 3 Fredrik Kuivinen
2005-09-07 16:50 ` [PATCH 1/2] Add '-i' flag to read-tree to make it ignore whats in the working directory Fredrik Kuivinen
2005-09-11  2:54   ` Unified merge driver pushed out to "master" branch Junio C Hamano
2005-09-11 21:05     ` Fredrik Kuivinen
2005-09-12  1:23       ` Junio C Hamano
2005-09-14  5:56     ` Another merge test case from the kernel tree Junio C Hamano
2005-09-14 16:11       ` Daniel Barkalow
2005-09-14 16:30         ` Junio C Hamano
2005-09-14 17:42       ` Fredrik Kuivinen
2005-09-14 17:51         ` Junio C Hamano
2005-09-15  0:47       ` Yet another set of merge test cases " Junio C Hamano
2005-09-19 16:13         ` Fredrik Kuivinen
2005-09-20  1:53           ` Junio C Hamano
2005-09-20  5:50             ` Fredrik Kuivinen
2005-09-07 16:51 ` [PATCH 2/2] A new merge algorithm Fredrik Kuivinen
2005-09-07 18:33 ` [PATCH 0/2] A new merge algorithm, take 3 Daniel Barkalow
2005-09-08  6:06   ` Fredrik Kuivinen
2005-09-08 15:27     ` Daniel Barkalow
2005-09-08 20:05       ` Fredrik Kuivinen
2005-09-08 21:27         ` Daniel Barkalow
2005-09-07 18:36 ` Junio C Hamano
     [not found]   ` <431F34FF.5050301@citi.umich.edu>
     [not found]     ` <7vvf1cz64l.fsf@assigned-by-dhcp.cox.net>
2005-09-08 15:06       ` Chuck Lever
2005-09-08 16:51         ` Junio C Hamano
2005-09-08 17:19           ` Linus Torvalds
2005-09-08 17:51             ` Junio C Hamano
2005-09-08 18:16             ` Chuck Lever [this message]
2005-09-08 18:35               ` Linus Torvalds
2005-09-08 18:58                 ` Chuck Lever
2005-09-08 20:59                   ` Linus Torvalds
2005-09-09  7:44                   ` [RFH] Merge driver Junio C Hamano
2005-09-09 16:05                     ` Daniel Barkalow
2005-09-09 16:43                       ` Junio C Hamano
2005-09-09 17:25                         ` Daniel Barkalow
2005-09-11  4:58                     ` Junio C Hamano
2005-09-12 21:08                     ` Fredrik Kuivinen
2005-09-12 21:16                       ` Junio C Hamano
2005-09-13 20:33                         ` Fredrik Kuivinen
2005-09-13 20:46                           ` Junio C Hamano
2005-09-08 20:54   ` [PATCH 0/2] A new merge algorithm, take 3 Junio C Hamano
2005-09-08 21:23     ` A Large Angry SCM

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