lkml.org 
[lkml]   [2015]   [Mar]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] workqueue: update numa affinity when node hotplug
On 2015/02/27 20:54, Tejun Heo wrote:
> Hello,
>
> On Fri, Feb 27, 2015 at 06:04:52PM +0800, Gu Zheng wrote:
>> Yasuaki Ishimatsu found that with node online/offline, cpu<->node
>> relationship is established. Because workqueue uses a info which was
>> established at boot time, but it may be changed by node hotpluging.
>
> I've asked this a couple times now but can somebody please justify why
> cpu<->node relationship needs to change? If it has to change, that's
> okay but let's please first make sure that we understand why such
> thing is necessary so that we can figure out what kind of facilities
> are necessary for such dynamism.
>
> Thanks.
>

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.

- 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.

Case B) Adding a node after removing another node, if pxm of them were different from
each other, cpu<->node relatiionship changes.

I personally thinks proper fix is building persistent cpu-id <-> lapicid relationship as
pxm does rather than creating band-aid.

But I have no good idea to hanlde case A), which is used now.
Hm, Case-A will not be problem for the case of workqueue's kmalloc because a node with
ZONE_NORMAL cannot be removed.

Thanks,
-Kame



\
 
 \ /
  Last update: 2015-03-02 10:01    [W:0.078 / U:3.820 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site