On 2020-11-24 01:04, Jakub Kicinski wrote:
On Thu, 19 Nov 2020 09:30:15 +0100 Björn Töpel wrote:+ /* The NAPI context has more processing work, but busy-polling + * is preferred. Exit early. + */ + if (napi_prefer_busy_poll(n)) { + if (napi_complete_done(n, work)) { + /* If timeout is not set, we need to make sure + * that the NAPI is re-scheduled. + */ + napi_schedule(n); + } + goto out_unlock; + }Do we really need to go through napi_complete_done() here? Isn't it sufficient to check: if (napi_prefer_busy_poll(n) && hrtimer_active(&n->timer)) // not 100% sure this is the // right helper for the check If timer is scheduled it will fire and worst case sirq will kick back in after timeout. napi_complete_done() should had been called by the driver already to schedule the timer. If the driver doesn't call napi_complete_done() we should not allow it to use busy_poll() anyway.
No, it's not. For a heavy traffic load, the napi_complete_done() will never be called by the driver. It'll just keep on spinning in the ksoftirqd. This code is to force out of that loop, so we need to call napi_complete_done() explicitly (which will set the timeout). Without the explicit napi_complete_done(), the ksoftirqd will not stop, and the busy-polling will never allow to enter. Björn
