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<p class="MsoNormal">The underlying model of the recent RDMA device reset patches was presented.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Reset flows are important for various use-cases, but their implementation for RDMA devices is challenging due to their stateful nature, and the fact that both kernel ULPs and user-space applications hold direct references to HW objects.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Support for kernel ULPs is provided by a new “error” state, in which devices do not process new WQEs or permit creation/modification of new resources, but flush any inflight WQEs and process Verb calls for destroying resources.<o:p></o:p></p>
<p class="MsoNormal">When a reset is required, the kernel provider issues a fatal event, resets the device, and places the device in error state.<o:p></o:p></p>
<p class="MsoNormal">It may then unregister the device, allowing all ULPs to process their standard shut-down flows.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Device resets are provider specific, and depend on whether the device is reachable.<o:p></o:p></p>
<p class="MsoNormal">If the device is unreachable, it is assumed that system FW will reset the device by other means (e.g., via PCI) before re-enabling access.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Support for user-space applications is provided by “zombifying” existing device instances.<o:p></o:p></p>
<p class="MsoNormal">Zombie devices maintain user-space references, but are not associated with HW. They persist as long as there are active handles to them, and do not permit any operation other than closing resources.<o:p></o:p></p>
<p class="MsoNormal">Some applications may hold references to zombie devices, while other applications hold valid handles to the same device after it recovered.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">We considered allowing applications a grace period to close their resources before being detached from the device by the kernel.<o:p></o:p></p>
<p class="MsoNormal">However, rapid recovery time was preferred.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Providers can add support for new HW by supporting the “error” state, and implementing the disassociate_ucontext() callback.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Finally, the notion of resetting devices while maintaining the ULP SW state was discussed.<o:p></o:p></p>
<p class="MsoNormal">It was deemed beneficial to maintain the ULP device representation (e.g., a SCSI adapter) within the OS while transient device resets are performed.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">--Liran<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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