linux-kernel - RE: [PATCH] staging: wfx: make a const array static, makes object smaller

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Date:   Mon, 19 Oct 2020 08:09:19 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Joe Perches' <joe@...ches.com>,
        Colin King <colin.king@...onical.com>,
        Jérôme Pouiller <jerome.pouiller@...abs.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>
CC:     "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] staging: wfx: make a const array static, makes object
 smaller

From: Joe Perches
> Sent: 17 October 2020 01:12
> 
> On Fri, 2020-10-16 at 23:33 +0100, Colin King wrote:
> > From: Colin Ian King <colin.king@...onical.com>
> >
> > Don't populate const array filter_ies on the stack but instead
> > make it static. Makes the object code smaller by 261 bytes.
> >
> > Before:
> >    text	   data	    bss	    dec	    hex	filename
> >   21674	   3166	    448	  25288	   62c8	drivers/staging/wfx/sta.o
> >
> > After:
> >    text	   data	    bss	    dec	    hex	filename
> >   21349	   3230	    448	  25027	   61c3	drivers/staging/wfx/sta.o
> 
> Thanks.
> 
> It's odd to me it's so large a change as it's only
> 24 bytes of initialization. (3 entries, each 8 bytes)

Perhaps the 'stack protector' crap?

Interestingly, loading the data from the 'readonly' section
is probably a data cache miss.
Which might end up being slower than the extra code to
update the on-stack data.
The extra code might get prefetched...

	David
 

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