On Thu, Feb 23, 2006 at 10:50:49PM +0100, Mostafa Z. Afgani wrote: > After the last kernel update (2.6.15-1.1831_FC4) the rt2500 (RaLink > WiFi) driver is causing the system to freeze on modprobe -- on > restarting the PC the boot process hangs and hence renders the machine > unusable. > > A post on the rt2x00 driver forum led me to the information that SMP is > enabled even on single processor FC kernels (at least from 2.6.15 on). I > just though it must be a mistake and dutifully filed a BUG report: > > https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=182640 > > But, within minutes of posting the report, I got a reply that the it is > NOTABUG & CLOSED! The reason provided was "The performance loss from > running SMP on a UP x86_64 machine is negligable." For FC4, this was a mistake. A regression that slipped in when rebasing a rawhide kernel to FC4 during the 2.6.15 transition. The update-in-progress (See http://people.redhat.com/davej/kernels/FC4/) has it reverted, and the UP kernel will behave as UP. > Now, what I don't understand is what good is SMP on a UP kernel?? If I > want SMP, I'll install the SMP kernel. I assume I'm not the only one who > needs to run a UP kernel to make certain hardware work that won't > otherwise work with SMP! Someone please tell me why anyone would want > SMP enabled on UP kernels? For FC5 and onward, for x86-64, there is no -smp kernel. There are a number of reasons for this - Cuts down on an extra set of images for the ISOs. - Increases code-coverage, Everyone runs the same code. - Is only a tiny performance hit, and work is underway to make this completely go away. - Over time, it'll become more difficult to buy a UP x86-64, when dual-core & hyperthreading become more widespread. If drivers don't work in SMP, they need to be fixed to do so. Dave
