Subject: [PATCH v3 1/6] iommu/core: split mapping to page sizes as supported by the hardware

From: [email-masked] (Roedel, Joerg)
Date: Tue, 27 Sep 2011 15:12:22 +0200

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

-- 
AMD Operating System Research Center

Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach
General Managers: Alberto Bozzo, Andrew Bowd
Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632