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Date: Fri, 25 Jul 2014 09:44:36 +0800 From: Jiang Liu <jiang.liu@...ux.intel.com> To: Nishanth Aravamudan <nacc@...ux.vnet.ibm.com> CC: Andrew Morton <akpm@...ux-foundation.org>, Mel Gorman <mgorman@...e.de>, David Rientjes <rientjes@...gle.com>, Mike Galbraith <umgwanakikbuti@...il.com>, Peter Zijlstra <peterz@...radead.org>, "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>, "Rafael J. Wysocki" <rjw@...ysocki.net>, Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org, Tony Luck <tony.luck@...el.com>, linux-mm@...ck.org, linux-hotplug@...r.kernel.org, linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org Subject: Re: [RFC Patch V1 30/30] x86, NUMA: Online node earlier when doing CPU hot-addition On 2014/7/25 7:30, Nishanth Aravamudan wrote: > On 11.07.2014 [15:37:47 +0800], Jiang Liu wrote: >> With typical CPU hot-addition flow on x86, PCI host bridges embedded >> in physical processor are always associated with NOMA_NO_NODE, which >> may cause sub-optimal performance. >> 1) Handle CPU hot-addition notification >> acpi_processor_add() >> acpi_processor_get_info() >> acpi_processor_hotadd_init() >> acpi_map_lsapic() >> 1.a) acpi_map_cpu2node() >> >> 2) Handle PCI host bridge hot-addition notification >> acpi_pci_root_add() >> pci_acpi_scan_root() >> 2.a) if (node != NUMA_NO_NODE && !node_online(node)) node = NUMA_NO_NODE; >> >> 3) Handle memory hot-addition notification >> acpi_memory_device_add() >> acpi_memory_enable_device() >> add_memory() >> 3.a) node_set_online(); >> >> 4) Online CPUs through sysfs interfaces >> cpu_subsys_online() >> cpu_up() >> try_online_node() >> 4.a) node_set_online(); >> >> So associated node is always in offline state because it is onlined >> until step 3.a or 4.a. >> >> We could improve performance by online node at step 1.a. This change >> also makes the code symmetric. Nodes are always created when handling >> CPU/memory hot-addition events instead of handling user requests from >> sysfs interfaces, and are destroyed when handling CPU/memory hot-removal >> events. > > It seems like this patch has little to nothing to do with the rest of > the series and can be sent on its own? > >> It also close a race window caused by kmalloc_node(cpu_to_node(cpu)), > > To be clear, the race is that on some x86 platforms, there is a period > of time where a node ID returned by cpu_to_node() is offline. > > <snip> > >> Signed-off-by: Jiang Liu <jiang.liu@...ux.intel.com> >> --- >> arch/x86/kernel/acpi/boot.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c >> index 3b5641703a49..00c2ed507460 100644 >> --- a/arch/x86/kernel/acpi/boot.c >> +++ b/arch/x86/kernel/acpi/boot.c >> @@ -611,6 +611,7 @@ static void acpi_map_cpu2node(acpi_handle handle, int cpu, int physid) >> nid = acpi_get_node(handle); >> if (nid != -1) { >> set_apicid_to_node(physid, nid); >> + try_online_node(nid); > > try_online_node() seems like it can fail? I assume it's a pretty rare > case, but should the return code be checked? > > If it does fail, it seems like there are pretty serious problems and we > shouldn't be onlining this CPU, etc.? > >> numa_set_node(cpu, nid); >> if (node_online(nid)) >> set_cpu_numa_mem(cpu, local_memory_node(nid)); > > Which means you can remove this check presuming try_online_node() > returned 0. Good suggestion, will try to enhance the error handling path. > > Thanks, > Nish > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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