virtio-devices: virtio-blk always tries signal used queue when receiving completion event #6672
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elainewu1222
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When the rate limit was reached it was possible for the notification to the guest to be lost since the logic to handle the notification was tightly coupled with processing the queue. The notification would eventually be triggered when the rate limit pool was refilled but this could add significant latency. Address this by refactoring the code to separate processing queue and signalling - the processing of the queue is suspended when the rate limit is reached but the signalling will still be attempted if needed (i.e. VIRTIO_F_EVENT_IDX is still considered.) Signed-off-by: wuxinyue <[email protected]> Signed-off-by: Rob Bradford <[email protected]>
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rbradford
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I made a change to your commit message (no code change) to reflect what was written in the PR body and to match the project style. Hopefully this works for you?
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@rbradford yes, quite clear. thx. |
liuw
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rbradford
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Currently, when finishing processing disk IO completion event, virtio-blk calls
process_queue_submit_and_signalif rate limit not reached. That's because to support notification suppression, the backend needs to work in a loop and process all available event in the queue until nothing remained.However, for case that
rate_limit_reached == true, the backend stop handling without sending frontend a signal. Though when rate limit refills, the backend will be able to send the signal when handlingRATE_LIMITER_EVENT, the signal is actually delayed for some time.This fix will make the backend able to send the signal immediately no matter rate limit is hit or not.