linux-kernel - Re: [GIT PULL] Ext3 latency fixes

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Message-ID: <20090406215034.GD3797@csclub.uwaterloo.ca>
Date:	Mon, 6 Apr 2009 17:50:34 -0400
From:	lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Theodore Tso <tytso@....edu>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [GIT PULL] Ext3 latency fixes

On Sat, Apr 04, 2009 at 10:18:20PM +0200, Ingo Molnar wrote:
> btw., just to insert some hard data: usability studies place the 
> acceptance threshold for delays to around 300 milliseconds.
> 
> If the computer does not 'respond' (in a real or a fake, visible or 
> audible way) to their input within 0.3 seconds they get annoyed 
> emotionally.

You mean like hitting 'skip commercial' on the remote, and 2 minutes later
when the commercials are almost over, then it happens.  Yeah users get a
bit peeved at that.  Fortunately that particularly behaviour is somewhat
rare.  5 to 10 seconds is more common and sometimes it works fine.

> It does not matter how complex it is for the kernel to solve this 
> problem, it does not matter how far away and difficult to access the 
> data is. If we are not absolutely latency centric in Linux, if we 
> spuriously delay apps that do supposedly simple-looking things the 
> user _will_ get annoyed and _will_ pick another OS.

I would have to get _very_ annoyed before that happened.  I would have
to find a less annoying OS to switch to as well.

> All things considered it is certainly a combined kernel and app 
> problem space to get there, but not being completely aware of its 
> importance in the kernel kills any chance of us ever having a 
> long-term solution.

Certainly my problems are likely to a large extent mythtv's fault.

-- 
Len Sorensen
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