Messages in this thread | | | Subject | Re: Question on handling managed IRQs when hotplugging CPUs | From | John Garry <> | Date | Tue, 5 Feb 2019 13:24:11 +0000 |
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On 04/02/2019 07:12, Hannes Reinecke wrote: > On 2/1/19 10:57 PM, Thomas Gleixner wrote: >> On Fri, 1 Feb 2019, Hannes Reinecke wrote: >>> Thing is, if we have _managed_ CPU hotplug (ie if the hardware >>> provides some >>> means of quiescing the CPU before hotplug) then the whole thing is >>> trivial; >>> disable SQ and wait for all outstanding commands to complete. >>> Then trivially all requests are completed and the issue is resolved. >>> Even with todays infrastructure. >>> >>> And I'm not sure if we can handle surprise CPU hotplug at all, given >>> all the >>> possible race conditions. >>> But then I might be wrong. >> >> The kernel would completely fall apart when a CPU would vanish by >> surprise, >> i.e. uncontrolled by the kernel. Then the SCSI driver exploding would be >> the least of our problems. >> > Hehe. As I thought.
Hi Hannes,
> > So, as the user then has to wait for the system to declars 'ready for > CPU remove', why can't we just disable the SQ and wait for all I/O to > complete? > We can make it more fine-grained by just waiting on all outstanding I/O > on that SQ to complete, but waiting for all I/O should be good as an > initial try. > With that we wouldn't need to fiddle with driver internals, and could > make it pretty generic.
I don't fully understand this idea - specifically, at which layer would we be waiting for all the IO to complete?
> And we could always add more detailed logic if the driver has the means > for doing so. >
Thanks, John
> Cheers, > > Hannes
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