Brad Templeton [EMAIL PROTECTED] wrote: > > Top can be misleading with HT. But my machine is also HT and it's only > 60% idle, not 80%. And it's faster. Do you have dual channel RAM? > Can that be making this big a difference? Can your video card be that > much faster? Could Mandrake be doing much better than FC3?
If you run the binary Fedora kernels, then one possible factor could be the 4G+4G address space patch that Fedora kernels are built with. This turns each copyin/copyout from a simple bcopy with a trap handler into bcopy + a complex vm remapping. This increases the cost of system calls, especially "simple" calls like gettimeofday, small reads, etc, because the cost of the copyin/copyout now dominates anything else that may be happening. This would not be much of a factor for large reads, for example. On a 3.06GHz P4 HTT system I have here, running stock a FC2 kernel (vmlinuz-2.6.5-1.358smp) lmbench's lat_syscall shows 2.4us for a "null" (getpid) syscall, and 3.25us for a read syscall. Compare this to a a 2.6.5 SMP kernel.org kernel with the traditional 3G+1G address space on the same machine, which shows 0.38us for a "null" syscall, and 0.46us for a read syscall. Admittedly this may not amount to much in the scheme of things, or things may have gotten better with FC3. I also do not know how often myth makes syscalls, as I'm waiting eagerly for the UPS man to deliver the components of my first box. Drew
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