On 4/22/15 5:25 PM, David Miller wrote:
> From: David Ahern <david.ahern@oracle.com>
> Date: Wed, 22 Apr 2015 17:19:23 -0600
>
>> Only thing left in my queue is optimized versions of the ffs / fls
>> families, but that patch is v9b specific, not M7.
>
> Something faster than the popc thing in arch/sparc/lib/ffs.S?

hmmm... i saw that, but wasn't clear 1) how it got inserted and 2) the 
overhead of a function call versus inline. Anyways, what I have is the 
same 3 instructions as an inline. But really the __ffs was just along 
for the ride; the focus was on __fls.

>
> Are you thinking of using "lzcnt"?  I wasn't impressed with the
> performance of that instruction last time I played around with it.

A comparison of what I hacked together is attached (columns too wide for 
inline). Data is from a T4-2. It shows lzcnt to be better for __fls, fls 
and fl64.


>
>> I'd like to put some attention on precise mode for perf counters; it
>> just has not bubbled to the top.
>
> That plus the backtrace deadlock thing we're discussing in another
> thread, that bug is irritating because your pagefault_disable() change
> should "just work".
>

oh, yes. forgot about that one. I spent too many hours trying to figure 
out why processes get killed with a sigbus. I added an option to perf 
tool to skip userspace chains until I can get back to it.