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

[Corinna Vinschen <vinschen at redhat dot com>]

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.


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
Red Hat