Messages in this thread | | | Date | Fri, 5 Sep 2003 13:59:38 -0400 | From | Jeff Garzik <> | Subject | Re: [PATCH] Use -fno-unit-at-a-time if gcc supports it |
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On Fri, Sep 05, 2003 at 07:27:15PM +0200, Andi Kleen wrote: > 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. [...] > I suspect that is true for a lot of core kernel code - everything > that is worth inlining is already inlined and for the rest it doesn't matter.
Definitely , agreed. In fact, we are moving in the opposite direction: looking into what we can un-inline...
> On the other hand a lot of driver code seems to be written without > manual consideration for inline. For that it may be worth it. But then > I would consider core kernel code to be more important than driver > code.
Modern network drivers seem fairly aware of it ;-)
> 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)
Agreed.
Jeff
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