From: Andy Shevchenko
Sent: 01 February 2021 13:49
On Sat, Jan 30, 2021 at 11:17:18AM -0800, Yury Norov wrote:
Similarly to bitmap functions, find_next_*_bit() users will benefit
if we'll handle a case of bitmaps that fit into a single word. In the
very best case, the compiler may replace a function call with a
single ffs or ffz instruction.
Would be nice to have the examples how it reduces the actual code size (based
on the existing code in kernel, especially in widely used frameworks /
subsystems, like PCI).
I bet it makes the kernel bigger but very slightly faster.
But the fact that the wrappers end up in the i-cache may
mean that inlining actually makes it slower for some calling
sequences.
If a bitmap fits in a single word (as a compile-time constant)
then you should (probably) be using different functions if
you care about performance.
David
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