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From: Nick Piggin <>
To: Jaya Kumar <>
Cc: Andrew Morton <>,,,
Subject: Re: [PATCH/RFC 2.6.20-rc4 1/1] fbdev,mm: hecuba/E-Ink fbdev driver
Date: Fri, 12 Jan 2007 11:47:30 +1100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Jaya Kumar wrote:
> On 1/11/07, Andrew Morton <> wrote:
>> That's all very interesting.
>> Please don't dump a bunch of new implementation concepts like this on us
>> with no description of what it does, why it does it and why it does it in
>> this particular manner.
> Hi Andrew,
> Actually, I didn't dump without description. :-) I had posted an RFC
> and an explanation of the design to the lists. Here's an archive link
> to that post. 
> I wasn't sure whether to include that description with the patch email
> because it was long.
>> From that email:
> ---
> This is there in order to hide the latency
> associated with updating the display (500ms to 800ms). The method used
> is to fake a framebuffer in memory. Then use pagefaults followed by delayed
> unmaping and only then do the actual framebuffer update. To explain this
> better, the usage scenario is like this:
> - userspace app like Xfbdev mmaps framebuffer
> - driver handles and sets up nopage and page_mkwrite handlers
> - app tries to write to mmaped vaddress
> - get pagefault and reaches driver's nopage handler
> - driver's nopage handler finds and returns physical page ( no
>  actual framebuffer )
> - write so get page_mkwrite where we add this page to a list
> - also schedules a workqueue task to be run after a delay
> - app continues writing to that page with no additional cost
> - the workqueue task comes in and unmaps the pages on the list, then
>  completes the work associated with updating the framebuffer

Have you thought about implementing a traditional write-back cache using
the dirty bits, rather than unmapping the page?

SUSE Labs, Novell Inc.
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  parent reply	other threads:[~2007-01-12  0:47 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-11 14:24 Jaya Kumar
2007-01-11 21:37 ` Andrew Morton
2007-01-12  0:22   ` Jaya Kumar
2007-01-12  0:36     ` Andrew Morton
2007-01-12  0:47     ` Nick Piggin [this message]
2007-02-17  9:47       ` Jaya Kumar
2007-01-12  7:15     ` Peter Zijlstra
2007-01-12  7:25       ` Andrew Morton

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