Messages in this thread | | | Date | Sat, 6 Sep 2003 09:08:54 +0200 | From | Jan Hubicka <> | Subject | Re: [PATCH] Use -fno-unit-at-a-time if gcc supports it |
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> > How much work would be to fix kernel in this regard? > > The big problem is that -funit-at-a-time is not widely used yet, > so even if we fix the kernel at some point it would likely > get broken again all the time by people who use older kernels > (= most kernel developers currently) > > > Are there some cases where this is esential? Kernel would be nice > > target to whole program optimization and GCC is not that far from it > > right now. > > I'm not sure that is that good an idea. When I was still hacking > TCP I especially moved some stuff out-of-line in the fast path to avoid > register pressure. Otherwise gcc would inline rarely used sub functions > and completely mess up the register allocation in the fast path. > Of course just a call alone messes up the registers somewhat because > of its clobbers, but a full inlining is usually worse.
You can use -O2 and rely on inline done by hand. I can add option -fno-inline-functions-called-once. That should avoid such a problems. Anyway it would be nice to mark functions that exist for this reason by noinline attribute so compiler knows about it, but that is different story. > > Also I fear cross module inlining would expose a lot of latent bugs > (missing barriers etc.) when the optimizer becomes more aggressive. > I'm not saying this would be a bad thing, just that it may be a lot > of work to fix (both for compiler and kernel people)
Some of this should be already tested by folks using Intel compiler I would hope.
Honza > > -Andi > - 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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