Re: What File System supports Application XIP

From: David Woodhouse (dwmw2_at_infradead.org)
Date: 09/09/04

  • Next message: Vinay Salotagi: "hi" 
    To: Paulo Marques <pmarques@grupopie.com>
Date:	Thu, 09 Sep 2004 10:42:57 +0100

    On Thu, 2004-09-09 at 10:19 +0100, Paulo Marques wrote:
    > colin wrote:
    > >
    > > Hi there,
    > > We are developing embedded Linux system. Performance is our consideration.
    > > We hope some applications can run as fast as possible,
    > > and are think if they can be put in a filesystem image, which resides in
    > > RAM, and run in XIP (eXecute In Place) manners.
    > > I know that Cramfs has supported Application XIP. Is there any other FS that
    > > also supports it? Ramdisk? Ramfs? Romfs?
    >
    > Obvisously cramfs can not support XIP, because the "in-place" image
    > is compressed (unless you have a processor that can execute compressed
    > code :)

    Actually there are hacks floating around which do let you use XIP with
    cramfs -- obviously you have to dispense with compression for the files
    you want to access that way.

    You won't gain at runtime by using XIP though. Your code and data will
    end up in RAM _whatever_ file system you use, and you'll be running from
    page cache.

    You may get a _slightly_ faster startup time after reboot if you use XIP
    from flash, because it doesn't have to be loaded into RAM first. But
    that comes at the cost of making it all a low slower during normal
    operation -- it's a lot slower to fetch icache lines from flash than it
    is from RAM.

    Arjan's right -- you almost certainly don't really want XIP. 

    -- 
dwmw2
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