* Paul Mackerras <pau...@samba.org> [2010-05-10 09:05:22]: > On Fri, May 07, 2010 at 05:18:42PM +0530, Vaidyanathan Srinivasan wrote: > > > These APIs take logical cpu number as input > > Change cpu_first_thread_in_core() to cpu_leftmost_thread_sibling() > > Change cpu_last_thread_in_core() to cpu_rightmost_thread_sibling() > > > > These APIs convert core number (index) to logical cpu/thread numbers > > Add cpu_first_thread_of_core(int core) > > Changed cpu_thread_to_core() to cpu_core_of_thread(int cpu) > > Why make all these changes? The end result doesn't seem any cleaner > or better than how it was before, and your patch description doesn't > give any reason for us to think "yes, we should make this change". > I assume you think this is a good change to make, so you need to > explain why it's a good idea and convince the rest of us.
Sure Paul.. let me explain. The crux of the issue is to make 'threads_per_core' accessible to the pseries_energy module. In the first RFC, I had directly exported the variable which is not a good design. Ben H suggested to make an API around it and then export the function: http://lists.ozlabs.org/pipermail/linuxppc-dev/2010-April/081610.html Instead of making an API to read threads_per_core, as Ben suggested, I have made a wrapper at a higher level to make an API to convert from logical cpu number to core number. The current APIs cpu_first_thread_in_core() and cpu_last_thread_in_core() returns logical CPU number while cpu_thread_to_core() returns core number or index which is not a logical CPU number. Ben recommended to clearly name them to distinguish 'core number' versus first and last 'logical cpu number' in that core. Hence in the new scheme, I have: > > Change cpu_first_thread_in_core() to cpu_leftmost_thread_sibling() > > Change cpu_last_thread_in_core() to cpu_rightmost_thread_sibling() which work on logical cpu numbers. While cpu_first_thread_of_core() and cpu_core_of_thread() work on core index. Example usage: (4 threads per core system) cpu_leftmost_thread_sibling(5) = 4 cpu_rightmost_thread_sibling(5) = 7 cpu_core_of_thread(5) = 1 cpu_first_thread_of_core(1) = 4 cpu_core_of_thread() is used in cpu_to_drc_index() in the module and cpu_first_thread_of_core() is used in drc_index_to_cpu() in the module. These APIs may be useful in other modules in future, and the proposed design is a good method to export these APIs to modules. An alternative approach could be to move both the base functions cpu_to_drc_index() and drc_index_to_cpu() into the kernel like in arch/powerpc/kernel/smp.c Thanks for the review, I hope I have explained the requirements and design for this cleanup. --Vaidy _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
