Messages in this thread | | | Date | Mon, 27 Feb 2006 18:33:55 -0500 | From | Bill Davidsen <> | Subject | Re: [Patch 4/4] Tell GCC 4.1 to move unlikely() code to a separate section |
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Andi Kleen wrote: > On Monday 27 February 2006 16:31, Arjan van de Ven wrote: >> This patch is more controversial I assume; it offers the option >> to use the gcc 4.1 option to move unlikely() code to a separate section. >> On the con side, this means that longer byte sequences are needed to jump >> to this code, on the Pro side it means that the unlikely() code isn't sharing >> icache cachelines and tlbs anymore. > > I don't think this will do anything because the default Makefile > still has > > CFLAGS += -fno-reorder-blocks > > That was me because it made assembly debugging much easier. I would be willing > to reconsider this if you can give me some hard data just from this change: > - benchmark changes > - .text size increase > > Also I don't like it being an separate CONFIG options. We already have too many > obscure ones. Either it should be on by default or not there at all.
I think you just made the case for an option, if it does produce substantially better code and justify being done, you still would want a way to kill it for debugging.
I'd like to see what it gains in general, and how much it depends on processor type and cache size. -- -bill davidsen (davidsen@tmr.com) "The secret to procrastination is to put things off until the last possible moment - but no longer" -me
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