On Fri, 16 Jun 2006, Chase Venters wrote: > On Fri, 16 Jun 2006, Andi Kleen wrote: > > > > > > To this last point, it might be more reasonable to map in a page that > > > contained a new structure with a stable ABI, which mirrored some of > > > the task_struct information, and likely other useful information as > > > needs are identified in the future. In any case, it would be hard > > > to beat a single memory read for performance. > > > > That would mean making the context switch and possibly other > > things slower. > > Well, if every process had a page of its own, what would the context switch > overhead be? Mostly copying the useful information into the read-only mapped page. However, this doesn't have to be all that expensive. The particular information we care about in this case only needs to be copied when a task begins running on a CPU different from the one it last ran on. In fact, on ia64 we already have something very similar to handle certain I/O pecularities on SN2. http://marc.theaimsgroup.com/?l=linux-ia64&m=113831137712197&w=2 That work could form the basis for a low-impact method of exporting the current CPU to user space via a read-only mapped page. I'll admit to having zero knowledge of whether this would be workable on anything other than ia64. Thanks, Brent -- Brent Casavant All music is folk music. I ain't bcasavan@xxxxxxx never heard a horse sing a song. Silicon Graphics, Inc. -- Louis Armstrong - : send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
![]() |