On Thu, Dec 20, 2001 at 05:22:12PM +0530, Bharata B Rao wrote: > On Thu, Dec 20, 2001 at 11:41:38AM +0000, John Levon wrote: > > On Wed, Dec 19, 2001 at 11:07:11AM +0530, Bharata B Rao wrote: > > > > > Please consider the following definitions from include/linux/irq_cpustat.h > > > -------------------------- > > > #ifdef CONFIG_SMP > > > #define __IRQ_STAT(cpu, member) (irq_stat[cpu].member) > > > #else > > > #define __IRQ_STAT(cpu, member) ((void)(cpu), irq_stat[0].member) > > > #endif > > > > I can only assume this is for performance. cpu might not be constant to the compiler, > > so the first would still have an indirection overhead on UP. The second one, however, > > lets the compiler optimise as the value of cpu is discarded (assume its evaluation has > > not side effects that is ;) > > If that is so, why not just > #define __IRQ_STAT(cpu, member) (irq_stat[0].member) > for UP, so that the macros like local_irq_count(cpu) can be used as Lvalue. > (I am concerned about not being able to use this as Lvalue in UP) haven't I just answered this above ? whether it makes a difference or not performance-wise is a different matter. IF you want it to change, you should prove that it makes no real difference. john -- "Unless everyone else on earth is attending meetings I haven't been told about." - /. paranoia at its finest -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ IRC Channel: irc.openprojects.net / #kernelnewbies Web Page: http://www.kernelnewbies.org/
