On Thursday, January 10, 2013 02:36:59 PM Peter Jeremy wrote: > On 2013-Jan-07 18:25:58 -0800, Barney Cordoba <barney_cord...@yahoo.com> wrote: > >I have a situation where I have to run 9.1 on an old single core > >box. Does anyone have a handle on whether it's better to build a non > >SMP kernel or to just use a standard SMP build with just the one > >core? > > Another input for this decision is kern/173322. Currently on x86, > atomic operations within kernel modules are implemented using calls > to code in the kernel, which do or don't use lock prefixes depending > on whethur the kernel was built as SMP. My proposed change changes > kernel modules to inline atomic operations but always include lock > prefixes (effectively reverting r49999). I'm appreciate anyone who > feels like testing the impact of this change.
Presumably a locked atomic op is cheaper than a function call then? The current setup assumes the opposite. I think we should actually do this for atomics in modules on x86: 1) If a module is built standalone, it should do whichever is cheaper: a function call or always use "LOCK". 2) If a module is built as part of the kernel build, it should use inlined atomics that match what the kernel does. Thus, modules built with a non-SMP kernel would use inlined atomic ops that do not use LOCK. We have a way to detect this now (some HAVE_FOO #define added in the past few years) that we didn't back when this bit of atomic.h was written. -- John Baldwin _______________________________________________ freebsd-net@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org"
