Hi Dave, thanks for your reply. On Wed, Feb 23, 2011 at 1:22 AM, Dave Hylands <dhylands@xxxxxxxxx> wrote: > Hi Murali, > > On Tue, Feb 22, 2011 at 9:27 PM, Murali N <nalajala.murali@xxxxxxxxx> wrote: >> Hi, >> can somebody explain me what "__get_cpu_var()" macro does? >> I try to understand this macro but i couldn't, its representation is weired!!! > > get_cpu_var returns the contents of a per-cpu variable. > > __get_cpu_var contains the actual machine-dependant implementation. It > looks like all of the architectures use the one in > asm-generic/percpu.h > > In general, all of the per-cpu data is gathered together into a > section. Multiple sections are allocated (one per CPU). I think that > the address of the variable is really the offset within the section, > and each allocated section is cache-line aligned. This offset is then > added to the "offset for my cpu" to come up with the final address of > the variable, which is dereferenced as a pointer dereference. There > are lots of extra doo-dads to get around warnings, and to prevent the > linker from producing relocation references for for the variable > access (since it looks like an access of a global variable, but it's > really just doing a game of using the offset of the variable within > the section). > > So you could think of it as a very fancy offsetof macro. > > There are several other macros involved, perhaps you could be a bit > more specific about your request? > > Dave Hylands > I have one more basic question. Why would we need to maintain structures like this? Is there any advantage we get here? I saw one of the architectures specifics timer code, through out the code they are using this macro. -- Regards, Murali N _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
