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RE: Execute-in-Place (XIP) from flash?



Thanks for the info Mikael!

> -----Original Message-----
> From: Mikael Starvik [mailto:mikael.starvik@xxxxxxx.com]
> Sent: Thursday, 23 September 2004 6:59 PM
> To: Fettahlioglu, Mahmut; Mikael Starvik
> Cc: dev-etrax
> Subject: RE: Execute-in-Place (XIP) from flash?
> 
> We have been running 2.4.26 (and even 2.4.27) internally for a while
> and it works at least as good as 2.4.22.
> 
> Most important changes:
> 
> Fixed an information leakage bug in the ethernet driver
> IDE driver updated to work for >= 2.4.21
> No more garabage when printing lots of debug from kernel
> Add support for isoc out in USB driver
> 
> /Mikael
> 
> -----Original Message-----
> From: Fettahlioglu, Mahmut [mailto:Mahmut.Fettahlioglu@xxxxxxx.au]
> Sent: Thursday, September 23, 2004 10:07 AM
> To: Mikael Starvik
> Cc: dev-etrax
> Subject: RE: Execute-in-Place (XIP) from flash?
> 
> 
> Thanks again Mikael.
> 
> I have asked this to the list before, but maybe I didn't put in down
> very
> clearly. I was asked to see if it is justifiable to move to 2.4.26 for
> our
> Etrax systems.
> 
> Is there a release notes or something similar that shows what the
> differences (if any) are between Axis driver patches you have for 2.4.22
> and
> 2.4.26? If no bugs that are relevant to us have been fixed in the new
> patch
> file, we will probably not make the move.
> 
> Thanks
> Mahmut
> 
> 
> > -----Original Message-----
> > From: Mikael Starvik [mailto:mikael.starvik@xxxxxxx.com]
> > Sent: Thursday, 23 September 2004 5:12 PM
> > To: 'Fettahlioglu, Mahmut'; dev-etrax
> > Subject: RE: Execute-in-Place (XIP) from flash?
> >
> > Hi!
> >
> > It is quite common to believe that swapping and pageing is the same
> > thing but it's not. You can never page out modified data and you
> > never need to swap out read-only data. So your conclussion is
> > correct that the benefit from a XIP solution would be low (except
> > from a performance view maybe).
> >
> > /Mikael
> >
> > -----Original Message-----
> > From: owner-dev-etrax@xxxxxxx.com">mailto:owner-dev-etrax@xxxxxxx.com] On
> Behalf
> > Of Fettahlioglu, Mahmut
> > Sent: Thursday, September 23, 2004 3:47 AM
> > To: dev-etrax
> > Subject: RE: Execute-in-Place (XIP) from flash?
> >
> >
> > Hi Mikael,
> >
> > I have been investigating this XIP option to see if it is a cheap and
> easy
> > way to cut down our memory usage. I was assuming the kernel would load
> the
> > entire binary and associated .so files to the RAM and execute them
> from
> > there. We have a system that currently needs a number of processes to
> run
> > concurrently, and any saving on RAM is welcome.
> >
> > We do not have a swap partition, so I was thinking process code
> segment
> > would never be swapped out. A google search confirmed Linux will
> discard
> > and
> > read back from disk such text and data segments as you have said, so
> there
> > is probably not much point in going XIP. The only gain would be the
> kernel
> > code segment could have been made to execute directly from flash, but
> this
> > is not required for us - 500k or so for the kernel is not an issue,
> and
> > not
> > to be able to reprogram the flash when kernel is running is much worse
> > than
> > saving this much ram.
> >
> > Thanks for clarifying this.
> >
> > Mahmut
> >
> > > -----Original Message-----
> > > From: Mikael Starvik [mailto:mikael.starvik@xxxxxxx.com]
> > > Sent: Tuesday, 21 September 2004 3:45 PM
> > > To: Fettahlioglu, Mahmut; Jonas Holmberg
> > > Cc: dev-etrax
> > > Subject: RE: Execute-in-Place (XIP) from flash?
> > >
> > > That is correct but I can't really see the point. Linux will page
> > > in pieces of the executable form flash to the page cache when a
> > > program is executed. If memory is low the program will be paged
> > > back to flash (except for dirty pages of cours).
> > >
> > > So for me there is two questions:
> > >
> > > 1. How are you going to tell the kernel that it should use XIP?
> > > 2. How will you benefit from it? One answer may be that you want
> > > to avoid pageing in and out for performance reasons.
> > >
> > > Even if you manage to do true XIP you will still have all the
> > > writable segments of the applications in RAM.
> > >
> > > Can you tell us more why you have so little RAM left but so
> > > much flash?
> > >
> > > /Mikael
> > >
> > > -----Original Message-----
> > > From: owner-dev-etrax@xxxxxxx.com">mailto:owner-dev-etrax@xxxxxxx.com] On
> > > Behalf Of Fettahlioglu, Mahmut
> > > Sent: Tuesday, September 21, 2004 3:56 AM
> > > To: Jonas Holmberg
> > > Cc: dev-etrax
> > > Subject: RE: Execute-in-Place (XIP) from flash?
> > >
> > >
> > > Thanks for the info Jonas.
> > >
> > > It looks like the only chip available for this project will be the
> > > internal
> > > flash. It will be alright to use it entirely as read-only. As long
> as I
> > > guarantee XIP processes do not run during FTP flash reprogramming it
> > > should
> > > work fine then?
> > >
> > > Thanks,
> > > Mahmut
> > >
> > > > -----Original Message-----
> > > > From: Jonas Holmberg [mailto:jonas.holmberg@xxxxxxx.com]
> > > > Sent: Monday, 20 September 2004 5:38 PM
> > > > To: Fettahlioglu, Mahmut
> > > > Cc: ETRAX development list
> > > > Subject: Re: Execute-in-Place (XIP) from flash?
> > > >
> > > > On Mon, Sep 20, 2004 at 01:56:45PM +1000, Fettahlioglu, Mahmut
> wrote:
> > > > > Hi all,
> > > > >
> > > > > I was wondering if there is a way I can use execute-in-place
> with
> > > > MCM4+16
> > > > > chips to save runtime memory. The options seem to be:
> > > > >
> > > > > - Use the internal flash "/etc" partition. This would involve
> > > formatting
> > > > the
> > > > > JFFS2 partition with something else e.g. FAT as JFFS2 uses
> > > compression.
> > > > >
> > > > > - Use an external USB flash ad run the software from there
> > > > >
> > > > > Do you think there are some limitations that prevent one or both
> of
> > > > these
> > > > > options? And if it can be done, do I need to change something in
> the
> > > > kernel
> > > > > for this?
> > > > >
> > > > > Any feedback welcome. Thanks to all,
> > > >
> > > > To be able to write to flash and do XIP at the same time you need
> more
> > > > than one chip. You must never write or erase the chip you execute
> code
> > > > from.
> > > >
> > > > /Jonas