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
