Re: [PATCH 2/9] IB: add a proper completion queue abstraction

Sagi Grimberg
2015-11-18T07:55:52Z

Hi Bart,

>> + */
>> +void ib_process_cq_direct(struct ib_cq *cq)
>> +{
>> + WARN_ON_ONCE(cq->poll_ctx != IB_POLL_DIRECT);
>> +
>> + __ib_process_cq(cq, INT_MAX);
>> +}
>> +EXPORT_SYMBOL(ib_process_cq_direct);
>
> My proposal is to drop this function and to export __ib_process_cq()
> instead (with or without renaming). That will allow callers of this
> function to compare the poll budget with the number of completions that
> have been processed and use that information to decide whether or not to
> call this function again.

I agree with that.

>
>> +static void ib_cq_poll_work(struct work_struct *work)
>> +{
>> + struct ib_cq *cq = container_of(work, struct ib_cq, work);
>> + int completed;
>> +
>> + completed = __ib_process_cq(cq, IB_POLL_BUDGET_WORKQUEUE);
>> + if (completed >= IB_POLL_BUDGET_WORKQUEUE ||
>> + ib_req_notify_cq(cq, IB_POLL_FLAGS) > 0)
>> + queue_work(ib_comp_wq, &cq->work);
>> +}
>> +
>> +static void ib_cq_completion_workqueue(struct ib_cq *cq, void *private)
>> +{
>> + queue_work(ib_comp_wq, &cq->work);
>> +}
>
> The above code will cause all polling to occur on the context of the CPU
> that received the completion interrupt. This approach is not powerful
> enough. For certain workloads throughput is higher if work completions
> are processed by another CPU core on the same CPU socket. Has it been
> considered to make the CPU core on which work completions are processed
> configurable ?

The workqueue is unbound. This means that the functionality you are
you are asking for exists.