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Date: Wed, 4 Dec 2002 12:19:47 +0100
From: Pavel Machek <pavel@suse.cz>
To: "David S. Miller" <davem@redhat.com>
Cc: ak@suse.de, linux-kernel@vger.kernel.org, hubicka@atrey.karlin.mff.cuni.cz
Subject: Re: [PATCH] Start of compat32.h (again)
Message-ID: <20021204111947.GB309@elf.ucw.cz>
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Hi!

>    > BTW, I bet your dynamic relocation tables are a bit larger too.
>    
>    Somewhat, but does it matter?  They are not kept in memory anyways.
> 
> It's all about how much data a ld.so relocation has to touch.  But
> preloading will help out here, even though that isn't in wide spread
> use just yet.
> 
> And I was talking about user stack usage, not the kernel kind
> :-)
> 
> Andi, do something very simple like run -m32 vs -m64 microbenchmarks,
> I bet -m32 beats -m64 in all the lmbench lat_proc tests.  On sparc64
> it's (on a 2-way SMP system):
> 
> -m32 fork+exit:		360.8328 microseconds
> -m32 fork+execve:	1342.2213 microseconds
> -m32 fork+/bin/sh:	5497.0149 microseconds
> 
> -m64 fork+exit:		553.9076 microseconds
> -m64 fork+execve:	1904.6315 microseconds
> -m64 fork+/bin/sh:	6268.6932 microseconds
> 
> NOTE: make sure you change /bin/sh to be 32-bit/64-bit as
>       appropriate in the tests above.
> 
> So what is this on x86_64? :-) I think lat_proc is great becuase it
> shows pure libc overhead in continually relocating the exit()
> etc. symbols in the child for fork+exit, for example.
> 
> The reason I'm making such a stink about this is that I don't want
> people believing that "the code generation improvements due to the
> extra x86_64 registers available nullifies the bloat cost from
> going to 64-bit"

Actually, it tends to nullify the bloat cost and then make it few
percent faster... For most of spec2000 modulo two or three cache-bound
tests that are 50% slower :-(.
								Pavel
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