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On 10/1/05, Dave Hansen <haveblue@us.ibm.com> wrote: > On Fri, 2005-09-30 at 16:33 +0900, Magnus Damm wrote: > > These patches implement NUMA memory node emulation for regular i386 PC:s. > > > > NUMA emulation could be used to provide coarse-grained memory resource control > > using CPUSETS. Another use is as a test environment for NUMA memory code or > > CPUSETS using an i386 emulator such as QEMU. > > This patch set basically allows the "NUMA depends on SMP" dependency to > be removed. I'm not sure this is the right approach. There will likely > never be a real-world NUMA system without SMP. So, this set would seem > to include some increased (#ifdef) complexity for supporting SMP && ! > NUMA, which will likely never happen in the real world. Yes, this patch set removes "NUMA depends on SMP". It also adds some simple NUMA emulation code too, but I am sure you are aware of that! =) I agree that it is very unlikely to find a single-processor NUMA system in the real world. So yes, "[PATCH 02/07] i386: numa on non-smp" adds _some_ extra complexity. But because SMP is set when supporting more than one cpu, and NUMA is set when supporting more than one memory node, I see no reason why they should be dependent on each other. Except that they depend on each other today and breaking them loose will increase complexity a bit. > Also, I worry that simply #ifdef'ing things out like CPUsets' update > means that CPUsets lacks some kind of abstraction that it should have > been using in the first place. An #ifdef just papers over the real > problem. Maybe. CPUSETS has two bitmaps, one for cpus and one for mems. So depending on SMP or NUMA seems logical to me. Regarding the #ifdef, it was added because partition_sched_domain() is only implemented for SMP. That symbol has no prototype or implementation when CONFIG_SMP is not set. Maybe it is better to add an empty inline function in linux/sched.h for !SMP? > I think it would likely be cleaner if the approach was to emulate an SMP > NUMA system where each NUMA node simply doesn't have all of its CPUs > online. Absolutely. And that removes the need for some of my patches. QEMU runs SMP kernels. It is possible to run SMP kernels on UP hardware. But there is of course a certain performance loss introduced by all the SMP locks. I'd rather not force !SMP users to run SMP kernels if they want coarse-grained memory resource control. Thanks for your input! / magnus - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | |||||||||
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