From: Linus Torvalds <torvalds@osdl.org>
To: Marco Costalba <mcostalba@gmail.com>
Cc: Git Mailing List <git@vger.kernel.org>,
Junio C Hamano <junkio@cox.net>, Alex Riesen <raa.lkml@gmail.com>,
Shawn Pearce <spearce@spearce.org>
Subject: Re: [RFC \ WISH] Add -o option to git-rev-list
Date: Mon, 11 Dec 2006 08:59:01 -0800 (PST) [thread overview]
Message-ID: <Pine.LNX.4.64.0612110855550.12500@woody.osdl.org> (raw)
In-Reply-To: <e5bfff550612102317w331f3b0fyc3c6b095ff21191a@mail.gmail.com>
On Mon, 11 Dec 2006, Marco Costalba wrote:
>
> These are tipical values (warm cache):
>
> $ time git rev-list --header --boundary --parents --topo-order HEAD | cat > /dev/null
> 3.67user 0.36system 0:04.29elapsed 93%CPU (0avgtext+0avgdata 0maxresident)k
> 0inputs+0outputs (0major+18033minor)pagefaults 0swaps
That's not timing what I asked. That's just timing the "git-rev-list". You
need to time the "cat" part too. Either use a script, or do something like
time sh -c "git-rev-list ... | cat > /dev/null".
> $ time git rev-list --header --boundary --parents --topo-order HEAD >
> /tmp/tmp.txt; cat /tmp/tmp.txt > /dev/null
> 3.44user 0.28system 0:03.74elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
> 0inputs+0outputs (0major+18033minor)pagefaults 0swaps
Again - you're only timing the _writer_, not the "cat" at all.
> For some reason the CPU *never* goes up 93% with pipe (while it's easy
> in the other two cases)
That's because you're only timing 93% of the work (ignoring the "cat"
part), and in the other cases you're ignoring the "cat" (that happens
_afterwards_, not concurrently) entirely.
> OK. I just don't understand how after waiting 100ms I get only 60KB
> and stay in the loop only one cycle instead of reading,
That's because the _writer_ will block. It notices that the reader cannot
read ass fast as it can write, so it blocks when its buffers fill up.
If you want to be fast, you need to be fast at reading. It's that simple.
next prev parent reply other threads:[~2006-12-11 17:00 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-12-10 11:38 [RFC \ WISH] Add -o option to git-rev-list Marco Costalba
2006-12-10 14:54 ` Alex Riesen
2006-12-10 18:16 ` Linus Torvalds
2006-12-10 19:51 ` Marco Costalba
2006-12-10 20:00 ` globs in partial checkout? Michael S. Tsirkin
2006-12-10 20:13 ` Linus Torvalds
2006-12-10 21:07 ` Michael S. Tsirkin
2006-12-10 20:08 ` [RFC \ WISH] Add -o option to git-rev-list Linus Torvalds
2006-12-10 20:19 ` Linus Torvalds
2006-12-10 22:05 ` Marco Costalba
2006-12-10 22:09 ` Marco Costalba
2006-12-10 22:16 ` Linus Torvalds
2006-12-10 22:35 ` Marco Costalba
2006-12-10 22:53 ` Linus Torvalds
2006-12-11 0:15 ` Marco Costalba
2006-12-11 0:51 ` Linus Torvalds
2006-12-11 7:17 ` Marco Costalba
2006-12-11 10:00 ` Alex Riesen
2006-12-11 16:59 ` Linus Torvalds [this message]
2006-12-11 17:07 ` Linus Torvalds
2006-12-11 17:39 ` Marco Costalba
2006-12-11 18:15 ` Linus Torvalds
2006-12-11 18:59 ` Marco Costalba
2006-12-11 19:25 ` Linus Torvalds
2006-12-11 20:28 ` Josef Weidendorfer
2006-12-11 20:40 ` Linus Torvalds
2006-12-11 20:54 ` Josef Weidendorfer
2006-12-11 21:14 ` Linus Torvalds
2006-12-15 18:45 ` Marco Costalba
2006-12-15 19:20 ` Linus Torvalds
2006-12-15 20:41 ` Marco Costalba
2006-12-15 21:04 ` Marco Costalba
2006-12-11 9:26 ` Josef Weidendorfer
2006-12-11 12:52 ` Marco Costalba
2006-12-11 13:28 ` Josef Weidendorfer
2006-12-11 17:28 ` Marco Costalba
2006-12-11 11:39 ` Andreas Ericsson
2006-12-11 12:59 ` Marco Costalba
2006-12-11 13:40 ` Andreas Ericsson
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