On 4/28/2012 8:55 PM, Al Viro wrote: > On Sat, Apr 28, 2012 at 05:46:13PM -0400, Chris Metcalf wrote: >>> For another, >>> there's kernel_execve() and if it fails (binary doesn't exist/has wrong >>> format/etc.) you'll get to .Lresume_userspace with EX1_PL(regs->ex1) >>> unchanged, i.e. the kernel one... >> This is a good point. The current syscall return path goes directly to >> .Lresume_userspace, which will screw up kernel syscalls. I think the right >> answer is still to jump to interrupt_return from those cases, though. In >> particular, this gets rid of the existing cruftiness where we have to >> document that a local label (.Lresume_userspace) can be the target of jumps >> from outside the containing function. > Point, but... Are you sure you want to add extra work to a very hot path? > Leaving the "we don't have any pending work to do" unburdened by that check > would reduce the overhead a lot. I suppose that's plausible; it's only 5 cycles of work (including the one cache-hot load), but might also be an extra icache line load, which could be quite a bit slower. I think the way to do this may be to both take your suggestion about checking user_mode() in do_work_pending(), and also handle the looping over the flag bits there as well. Then we can load the caller-saves once, prior to calling do_work_pending(), and when we return we're guaranteed to have interrupts disabled and TIF_ALLWORK clear. -- Chris Metcalf, Tilera Corp. http://www.tilera.com -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
