| Re: [PATCH v7 09/10] IPC: message queue copy feature introduced [message #48506 is a reply to message #48505] |
Fri, 19 October 2012 07:44  |
Stanislav Kinsbursky
Messages: 683
Registered: October 2011
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Senior Member |
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19.10.2012 04:52, Eric W. Biederman пишет:
> Stanislav Kinsbursky <skinsbursky@parallels.com> writes:
>
>> It's not just an optimisation.
>> If crtools will fail (with SIGSEGV, for instance), then queue will be empty.
>
> Regardless of what you call the benefit of this enhancement, this
> enhancement is not required to implement checkpoint/restart.
>
> For reliability/restartability I suspect a simple enqueue/dequeue loop
> over each message in the queue would be nearly as proof against SIGSEGV
> and other failures.
>
"Nearly as proof" is not good enough for CRIU quality of service.
Moreover, if crtools will fail in this loop, then not only one message will be
lost, but also the queue messages order will be invalid.
> So since all of these changes are enhancements we need to know what we
> are getting, over just sticking with the existing interfaces.
>
> Unless there is a real bottleneck for something to work, I suspect the
> direction forward is to make checkpoint and restart work with the
> existing kernel interfaces and then revisit that decision when you
> actually have a real problem.
>
> Eric
>
--
Best regards,
Stanislav Kinsbursky
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