Messages in this thread | | | Date | Tue, 22 Nov 2005 12:26:23 -0500 | From | Benjamin LaHaise <> | Subject | Re: rfc/rft: use r10 as current on x86-64 |
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On Tue, Nov 22, 2005 at 06:10:42PM +0100, Andi Kleen wrote: > I think you could get most of the benefit by just dropping > the volatile and "memory" from read_pda(). With that gcc would > usually CSE current into a register and it would would work essentially > the same way with only minor more .text overhead, but r10 would be still > available. > > Unfortunately when that's done then the kernel doesn't boot. > It's probably something silly, but i never had time to track it down. > Might want to look into that?
Without even fixing it, the difference in kernel code size is still 20K less than what using a register does. The benefit of using a register is that accessing a field in current can simply offset the register, compared to the pda usage that requires loading current into a register before the offset is performed. Using 'size' on the resulting kernels shows:
text data bss dec hex filename 4132289 819632 317256 5269177 5066b9 vmlinux.orig 4119951 819632 317256 5256839 503687 vmlinux.non-volatile 4097300 819560 317256 5234116 4fddc4 vmlinux.r10
I think that using a register makes more sense given the benefits.
-ben -- "Time is what keeps everything from happening all at once." -- John Wheeler Don't Email: <dont@kvack.org>. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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