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Date: Sat, 14 Nov 2015 08:13:44 +0100 From: Christoph Hellwig <hch@....de> To: Jason Gunthorpe <jgunthorpe@...idianresearch.com> Cc: Bart Van Assche <bart.vanassche@...disk.com>, Christoph Hellwig <hch@....de>, linux-rdma@...r.kernel.org, sagig@....mellanox.co.il, axboe@...com, linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 2/9] IB: add a proper completion queue abstraction On Fri, Nov 13, 2015 at 03:06:36PM -0700, Jason Gunthorpe wrote: > Looking at that thread and then at the patch a bit more.. > > +void ib_process_cq_direct(struct ib_cq *cq) > [..] > + __ib_process_cq(cq, INT_MAX); > > INT_MAX is not enough, it needs to loop. > This is missing a ib_req_notify also. No. Direct cases _never_ calls ib_req_notify. Its for the case where the SRP case polls the send CQ only from the same context it sends for without any interrupt notification at al. > +static int __ib_process_cq(struct ib_cq *cq, int budget) > + while ((n = ib_poll_cq(cq, IB_POLL_BATCH, cq->wc)) > 0) { > > Does an unnecessary ib_poll_cq call in common cases. I'd suggest > change the result to bool and do: > > // true return means the caller should attempt ib_req_notify_cq > while ((n = ib_poll_cq(cq, IB_POLL_BATCH, cq->wc)) > 0) { > for (...) > if (n != IB_POLL_BATCH) > return true; > completed += n; > if (completed > budget) > return false; > } > return true; > > And then change call site like: > > static void ib_cq_poll_work(struct work_struct *work) > { > if (__ib_process_cq(...)) > if (ib_req_notify_cq(cq, IB_POLL_FLAGS) == 0) > return; > // Else we need to loop again. > queue_work(ib_comp_wq, &cq->work); > } > > Which avoids the rearm. > > void ib_process_cq_direct(struct ib_cq *cq) > { > while (1) { > if (__ib_process_cq(..) && > ib_req_notify_cq(cq, IB_POLL_FLAGS) == 0) > return; > } > } > > Which adds the inf loop and rearm. > > etc for softirq For the workqueue and softirq cases this looks reasonable. For the direct case there is no rearming, though. > Perhaps ib_req_notify_cq should be folded into __ib_process_cq, then > it can trivially honour the budget on additional loops from > IB_CQ_REPORT_MISSED_EVENTS. Which also defeats this proposal. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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