Date: Sat, 24 Dec 2011 11:27:59 +0000 From: Alexander Best <arundel@freebsd.org> To: Bruce Evans <brde@optusnet.com.au> Cc: freebsd-current@freebsd.org, freebsd-arch@freebsd.org Subject: Re: [rfc] removing -mpreferred-stack-boundary=2 flag for i386? Message-ID: <20111224112759.GA25716@freebsd.org> In-Reply-To: <20111224220705.H2059@besplex.bde.org> References: <20111223235642.GA37495@freebsd.org> <20111224160050.T1141@besplex.bde.org> <20111224091250.GA9921@freebsd.org> <20111224220705.H2059@besplex.bde.org>
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On Sat Dec 24 11, Bruce Evans wrote: > On Sat, 24 Dec 2011, Alexander Best wrote: > > >On Sat Dec 24 11, Bruce Evans wrote: > >>On Fri, 23 Dec 2011, Alexander Best wrote: > >> > >>>is -mpreferred-stack-boundary=2 really necessary for i386 builds any > >>>longer? > >>>i built GENERIC (including modules) with and without that flag. the > >>>results > >>>are: > >> > >>The same as it has always been. It avoids some bloat. > >> > >>>1654496 bytes with the flag set > >>>vs. > >>>1654952 bytes with the flag unset > >> > >>I don't believe this. GENERIC is enormously bloated, so it has size > >>more like 16MB than 1.6MB. Even a savings of 4K instead of 456 bytes > > > >i'm sorry. i used du(1) to get those numbers, so i believe those numbers > >represent the ammount of 512-byte blocks. if i'm correct GENERIC is even > >more bloated than you feared and almost reaches 1GB: > > > >807,859375 megabytes with flag set > >vs. > >808,0820313 megabytes without the flag set > > That's certainly bloated. It counts all object files and modules, and > probably everything is compiled with -g. I only counted kernel text > size. yeah, but for demonstrating the different size between the build with -mpreferred-stack-boundary=2 set and -mpreferred-stack-boundary=2 unset, it doesn't really matter how big the directories are and if object files are included. the difference in size is < 1 megabyte. so setting -mpreferred-stack-boundary=2 doesn't aid in reducing the kernel (or modules) size, but merely to improve improve stack performance/efficiency. cheers. alex > > Bruce
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