On Fri, 04 May 2007 10:36:37 +0200 "Julio M. Merino Vidal" <[EMAIL PROTECTED]> wrote:
> > Anyway, what do you think about adding the above text to the code (percpu.h > maybe) as documentation? See the patch below. (Dunno if the Signed-off-by > line is appropriate as most of the text is yours.) > > Signed-off-by: Julio M. Merino Vidal <[EMAIL PROTECTED]> > > diff --git a/include/linux/percpu.h b/include/linux/percpu.h > index 600e3d3..b8e8b8c 100644 > --- a/include/linux/percpu.h > +++ b/include/linux/percpu.h > @@ -1,6 +1,21 @@ > #ifndef __LINUX_PERCPU_H > #define __LINUX_PERCPU_H > > +/* > + * percpu provides a mechanism to define variables that are specific to > each > + * CPU in the system. > + * > + * Each variable is defined as an independent array of NR_CPUS elements. > + * This approach is used instead of a per-CPU structure because it has the > + * following advantages: > + * - Independent maintenance: a source file can define new per-CPU > + * variables without distorting others. > + * - Fast access and relatively compact code. > + * - Avoids false sharing by keeping cache lines of different CPUs > separate. > + * - Doesn't waste a lot of memory in padding like NR_CPUs arrays usually > + * need to to avoid the previous point. > + */ > + > #include <linux/spinlock.h> /* For preempt_disable() */ > #include <linux/slab.h> /* For kmalloc() */ > #include <linux/smp.h> Documentation is good, and percpu probably misses one, but please add it in a Documentation/percpu.txt file, because it's the right place. You then can really have an extensive documentation, and you wont slow down kernel compiles... I suggest you document all variants (get_cpu_var(), __get_cpu_var(), ...) with examples of use Also, please note that per cpu data is not allocated * NR_CPUS, but depends on possible cpus. So if you boot an SMP kernel on a one CPU desktop, kernel allocates only the needed space. So per_cpu data has also a space saving argument against structures declared with [NR_CPUS] arrays. Thank you - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
