Messages in this thread | | | Date | Tue, 27 Sep 2011 15:12:22 +0200 | From | "Roedel, Joerg" <> | Subject | Re: [PATCH v3 1/6] iommu/core: split mapping to page sizes as supported by the hardware |
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On Tue, Sep 27, 2011 at 08:26:29AM -0400, Ohad Ben-Cohen wrote: > > With an unsigned long you can use plain and fast bit_ops instead of the > > full bitmap functions. > > Not sure I follow; the only bit operation I'm using while mapping is > find_next_bit() (which is a bitops.h method). > > What other faster variant are you referring to ?
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 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.
Joerg
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