On Fri, 8 Nov 2013, Stephen Boyd wrote: > If we're running on a v7 ARM CPU, detect if the CPU supports the > sdiv/udiv instructions and replace the signed and unsigned > division library functions with an sdiv/udiv instruction. > > Running the perf messaging benchmark in pipe mode > > $ perf bench sched messaging -p > > shows a modest improvement on my v7 CPU. > > before: > (5.060 + 5.960 + 5.971 + 5.643 + 6.029 + 5.665 + 6.050 + 5.870 + 6.117 + > 5.683) / 10 = 5.805 > > after: > (4.884 + 5.549 + 5.749 + 6.001 + 5.460 + 5.103 + 5.956 + 6.112 + 5.468 + > 5.093) / 10 = 5.538 > > (5.805 - 5.538) / 5.805 = 4.6% > > Signed-off-by: Stephen Boyd <sb...@codeaurora.org>
Bah..... NAK. We are doing runtime patching of the kernel for many many things already. So why not do the same here? The obvious strategy is to simply overwrite the start of the existing __aeabi_idiv code with the "sdiv r0, r0, r1" and "bx lr" opcodes. Similarly for the unsigned case. That let you test the hardware capability only once during boot instead of everytime a divide operation is performed. Nicolas -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
