In message <[EMAIL PROTECTED]> you wro te: > Hi all, > I am trying to optimize the __copy_tofrom_user function for PPC4xx, > and I would want to know why the exception handling code has been made > so complicated. All the fixup code should do is to store the number of > bytes that failed in copy in r3 and return back. > > The current code tries to copy one byte at a time after read fault. I > don't understand why that is necessary. It then clears out the > destination. All these logic has made the code very unfriendly to > read.
Would a multibyte read be guaranteed to be aligned? > I have a version which just keeps a count of bytes copied till any > fault happened. Then for any exception, I just substract this value > from the total number of bytes to be copied, and store in r3 and > return back. This is the common fixup code for all paths. It makes the > fixup code much more readable like other architectures (eg. x86). > > My questions are: > 1) Why do we need to distinguish between load and store failure? If > either load or store fails, the copy did not go thru. But the code > sets r9 to 0 for load failure, and r9 to 1 for write failure. Why do > we need to care for that? > > 2) For read failure, why do we clear out the destination (lines 509 to > 529 in arch/powerpc/lib/copy_32.S)? Other architecture don't do that. Which version of the code are you referring to here? Can you give us a git SHA1? Clean up patches are welcome. Maybe it would be best to post what you have as an RFC patch. Then people can take a closer/easier look at your cleanups and/or try them out. Mikey > > I would appreciate any comments. > > Thanks, > Prodyut > _______________________________________________ > Linuxppc-dev mailing list > Linuxppc-dev@ozlabs.org > https://ozlabs.org/mailman/listinfo/linuxppc-dev > _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
