RE: [PATCH newlib]New configuration option disable io vector buffer in Newlib

["Bin Cheng" <bin dot cheng at arm dot com>]

> -----Original Message-----
> From: newlib-owner@sourceware.org [mailto:newlib-owner@sourceware.org] On
> Behalf Of Corinna Vinschen
> Sent: Wednesday, March 27, 2013 5:07 PM
> To: newlib@sourceware.org
> Subject: Re: [PATCH newlib]New configuration option disable io vector buffer
> in Newlib
> 
> On Mar 27 15:33, Bin Cheng wrote:
> > > -----Original Message-----
> > > From: newlib-owner@sourceware.org
> > > [mailto:newlib-owner@sourceware.org] On Behalf Of Howland Craig D
> > > (Craig)
> > > Sent: Tuesday, March 26, 2013 9:25 PM
> > > To: newlib@sourceware.org
> > > Subject: RE: [PATCH newlib]New configuration option disable io
> > > vector
> > buffer
> > > in Newlib
> > >
> > > > From: newlib-owner@sourceware.org
> > > > [mailto:newlib-owner@sourceware.org]
> > > On Behalf Of Bin Cheng
> > > > Sent: Tuesday, March 26, 2013 6:14 AM
> > > >
> > > > Hi,
> > > > Stream IO functions in Newlib construct structures like
> > > > __suio/__siov,
> > > then
> > > > call function __sfvwrite_r to do the buffered IO. From the view of
> > > > MCU programs, this layer code of vector buffer occupies large
> > > > amount flash
> > > and
> > > > is generally unnecessary. So here this patch introduces a new
> > > configuration
> > > > time option "--disable-newlib-fvwrite-in-streamio" allowing user
> > > > to
> > > disable
> > > > io vector buffer in Newlib, thus reduces foot-print of stream-io
> > > > and formatted IO.
> > > > ... It has also been applied in the release of "GNU Tools for ARM
> > > Embedded
> > > > Processors" and used in many projects I believe.
> > > >
> > > > Is it OK or any suggestions?
> > >
> > > Can you provide numbers of how much size savings were realized?
> > >
> > > Is there also a run-time efficiency gain because a layer has been removed?
> > >
> > > I suggest that an explanation of this new option with its benefits
> > > and drawbacks be added somewhere.  (Does it rate mention in HOWTO?)
> > > It's easy
> > to
> > > envision that a new user comes to take Newlib 3 months from now, and
> > > would
> > not
> > > even know that this option existed.  And even if they were to read
> > configure,
> > > the "disable iov in streamio" description would mean little or
> > > nothing to
> > most
> > > people.
> > >
> >
> > Thanks for suggestions. As for the changes:
> > For code size, this patch reduces about 2+KB text section with below
> > command line for a simple formatted IO program:
> > $ arm-none-eabi-gcc -mthumb -mcpu=cortex-m0 -Os -ffcuntion-sections
> > -fdata-sections -Wl,--gc-sections -lc -lnosys -lc main.c -o main.exe
> >
> > The library itself is build with "-Os -ffunction-sections -fdata-sections".
> >
> > For performance, I measured a formatted IO test which calls lots of
> > "snprintf" and runs for about 10Secs. Turns out this patch can improve
> > performance about 5~6%, but I won't claim how good the patch is
> > because it's just one use-case.
> >
> > As for how-to document, I am not sure how to handle it. There are a
> > bunch of "--disable/enable-*" options, but neither HOWTO nor README mentions
> them.
> > Maybe we could re-factor the document and find a place to describe
> > these options in detail.
> 
> Yes, that's a bummer.  I think we could really need somebody who would be
> willing to add all these options to the README file with a bit of explanation
> what each of them is doing.
> 

I did investigation on how those options work before, maybe I can take this work later. I have some other patches to reduce code size, I can get back to this once I finish them.

Thanks.