Messages in this thread | | | Date | Tue, 26 Sep 2006 18:27:58 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [PATCH] Linux Kernel Markers 0.14 for 2.6.17 |
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* Jeremy Fitzhardinge (jeremy@goop.org) wrote: > Mathieu Desnoyers wrote: > >Hi, > > > >Constructing on Jeremy Fitzhardinge's comments about gcc optimizations, I > >rewrote (once more) the markers mechanism so that the optimized mode does > >not > >jump between two different inline asm. Instead, the optimized version uses > >a > >load immediate (in assembly) that will be used by a test to decide of a > >branch > >(in C). > > > > I should have spelled out my point a bit more. If you've got a flag > you're just testing, couldn't you just do: > > if (__mark_enabled_##name) > (*__mark_func)(...); > > and do without the asms or the section? >
Because a supplementary memory read is added on the critical path with a normal flag test. The assembly can provide an immediate value without any need of memory read from the data section.
To change the behavior of the program, I just have to change the immediate value in the movb instruction.
However, the non-optimized generic version does exactly this : it simply tests a flag loaded from memory. It can be very useful on embedded systems where the code is in read-only memory.
Regards,
Mathieu
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