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Date: Tue, 3 Mar 2015 15:53:46 +0900 From: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com> To: Tejun Heo <tj@...nel.org> CC: Gu Zheng <guz.fnst@...fujitsu.com>, <linux-kernel@...r.kernel.org>, <laijs@...fujitsu.com>, <isimatu.yasuaki@...fujitsu.com>, <tangchen@...fujitsu.com> Subject: Re: [PATCH] workqueue: update numa affinity when node hotplug On 2015/03/03 1:28, Tejun Heo wrote: > Hello, > > On Mon, Mar 02, 2015 at 05:41:05PM +0900, Kamezawa Hiroyuki wrote: >> Let me start from explaining current behavior. >> >> - cpu-id is determined when a new processor(lapicid/x2apicid) is founded. >> cpu-id<->nodeid relationship is _not_ recorded. > > Is this something from the firmware side or is it just that we aren't > maintaining the association right now? > I think it's not just maintained. >> - node-id is determined when a new pxm(firmware info) is founded. >> pxm<->nodeid relationship is recorded. >> >> By this, there are 2 cases of cpu<->nodeid change. >> >> Case A) In x86, cpus on memory-less nodes are all tied to existing nodes(round robin). >> At memory-hotadd happens and a new node comes, cpus are moved to a newly added node >> based on pxm. > > Ah, okay, so the firmware doesn't provide proximity information at all > for memory-less nodes so we end up putting all of them somewhere > random and when memory is added to one of the memory-less nodes, the > mapping information changes? > With memory-less node, proximity domain for processors are given but ignored. When memory(node) hotplug happens, the information revisited and cpuid<->nodeid relationship is updated. > Am I understanding it correctly? If so, it's super weird tho. Why > wouldn't there be proximity information for a memless node? Not > having memory doesn't mean it's at the same distance from all existing > nodes. > Firmware gives pxm for memory-less node but it's ignored. I'm not sure why the current implemetaion is. >> Case B) Adding a node after removing another node, if pxm of them were different from >> each other, cpu<->node relatiionship changes. > > I don't get this either. Does proximity relationship actually change? > Or is it that we're assigning different IDs to the same thing?Isn't > proximity pretty much hardwired to how the system is architected to > begin with? > relationship between proximity domain and lapic id doesn't change. relationship between lapic-id and cpu-id changes. pxm <-> memory address : no change pxm <-> lapicid : no change pxm <-> node id : no change lapicid <-> cpu id : change. >> I personally thinks proper fix is building persistent cpu-id <-> lapicid relationship as >> pxm does rather than creating band-aid. > > Oh if this is possible, I agree that's the right direction too. > Implementation is a bit complicated now :(. Thanks, -Kame > Thanks. > -- 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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