On 01/04, Nicolas Pitre wrote: > On Mon, 4 Jan 2016, Stephen Boyd wrote: > > > > I can update the patches to be based on this patch here and > > handle the conditional branches and tail call optimization cases > > by adding some safety checks like we have for the ftrace branch > > patching. But I'd rather not do that work unless we all agree > > that it's worthwhile pursuing it. > > > > Is there still any concern about the benefit of patching each > > call site vs. patching the functions? The micro benchmark seems > > to show some theoretical improvement on cortex-a7 and I can run > > it on Scorpion and Krait processors to look for any potential > > benefits there, but I'm not sure of any good kernel benchmark for > > this. If it will be rejected due to complexity vs. benefit > > arguments I'd rather work on something else. > > You could run the benchmark on Scorpion and Krait to start with. If > there is no improvement what so ever like on A15's then the answer might > be rather simple. > So running the benchmark on Scorpion is not useful because we don't have the idiv instruction there. On Krait I get the following results. I ran this on a dragonboard apq8074 with maxcpus=1 on the kernel command line. Testing INLINE_DIV ... real 0m 13.56s user 0m 13.56s sys 0m 0.00s Testing PATCHED_DIV ... real 0m 15.15s user 0m 15.14s sys 0m 0.00s Testing OUTOFLINE_DIV ... real 0m 18.09s user 0m 18.09s sys 0m 0.00s Testing LIBGCC_DIV ... real 0m 24.26s user 0m 24.25s sys 0m 0.00s It looks like the branch actually costs us some time here. Patching isn't as good as the compiler inserting the instruction itself, but it is better than branching to the division routine. -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
