Re: [PATCH v3 1/6] iommu/core: split mapping to page sizes assupported by the hardware

[Ohad Ben-Cohen]

On Tue, Sep 27, 2011 at 4:12 PM, Roedel, Joerg <Joerg.Roedel@xxxxxxx> wrote:
> You pass a pointer to an unsigned long for the page-size bitmap. This
> allows to use an array of unsigned long. But a single unsigned long is
> sufficient

This is fine; I can change that if you like it better (though without
doing the change below this is probably moot).

> and you can use functions like ffs() and fls() together with
> shifting. These functions often translate to a single intruction in the
> binary. The find_next_bit function has much more overhead because it
> needs to handle the array-of-ulong case.

So you're suggesting to re-implement find_next_bit() using ffs()/fls()
and shifting ?

What's the point ?

Sure, if we'll have a proven performance issue while using
find_next_bit() we can think of doing this, but at this stage, this
sounds to me like a premature optimization which isn't too elegant.

At this point I strongly prefer readable, maintainable and easier to
debug code over optimization which isn't proven to be necessary.

Thanks,
Ohad.
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