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SubjectRe: [PATCH] RDMA/core: reduce IB_POLL_BATCH constant
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On 2/28/2018 12:09 AM, Jason Gunthorpe wrote:
> On Thu, Feb 22, 2018 at 05:39:09PM +0200, Sagi Grimberg wrote:
>>
>>>> The only reason why I added this array on-stack was to allow consumers
>>>> that did not use ib_alloc_cq api to call it, but that seems like a
>>>> wrong decision when thinking it over again (as probably these users
>>>> did not set the wr_cqe correctly).
>>>>
>>>> How about we make ib_process_cq_direct use the cq wc array and add
>>>> a WARN_ON statement (and fail it gracefully) if the caller used this
>>>> API without calling ib_alloc_cq?
>>>
>>> but we tried to avoid cuncurrent access to cq->wc.
>>
>> Not sure its a valid use-case. But if there is a compelling
>> reason to keep it as is, then we can do smaller on-stack
>> array.
>
> Did we come to a conclusion what to do here?

guys,
what do you think about the following solution (untested):


diff --git a/drivers/infiniband/core/cq.c b/drivers/infiniband/core/cq.c
index bc79ca8..59d2835 100644
--- a/drivers/infiniband/core/cq.c
+++ b/drivers/infiniband/core/cq.c
@@ -17,6 +17,7 @@

/* # of WCs to poll for with a single call to ib_poll_cq */
#define IB_POLL_BATCH 16
+#define IB_POLL_BATCH_DIRECT 8

/* # of WCs to iterate over before yielding */
#define IB_POLL_BUDGET_IRQ 256
@@ -25,17 +26,25 @@
#define IB_POLL_FLAGS \
(IB_CQ_NEXT_COMP | IB_CQ_REPORT_MISSED_EVENTS)

-static int __ib_process_cq(struct ib_cq *cq, int budget, struct ib_wc
*poll_wc)
+static int __ib_process_cq(struct ib_cq *cq, int budget, struct ib_wc
*poll_wc,
+ int batch)
{
- int i, n, completed = 0;
- struct ib_wc *wcs = poll_wc ? : cq->wc;
-
+ int i, n, ib_poll_batch, completed = 0;
+ struct ib_wc *wcs;
+
+ if (poll_wc) {
+ wcs = poll_wc;
+ ib_poll_batch = batch;
+ } else {
+ wcs = cq->wc;
+ ib_poll_batch = IB_POLL_BATCH;
+ }
/*
* budget might be (-1) if the caller does not
* want to bound this call, thus we need unsigned
* minimum here.
*/
- while ((n = ib_poll_cq(cq, min_t(u32, IB_POLL_BATCH,
+ while ((n = ib_poll_cq(cq, min_t(u32, ib_poll_batch,
budget - completed), wcs)) > 0) {
for (i = 0; i < n; i++) {
struct ib_wc *wc = &wcs[i];
@@ -48,7 +57,7 @@ static int __ib_process_cq(struct ib_cq *cq, int
budget, struct ib_wc *poll_wc)

completed += n;

- if (n != IB_POLL_BATCH ||
+ if (n != ib_poll_batch ||
(budget != -1 && completed >= budget))
break;
}
@@ -72,9 +81,9 @@ static int __ib_process_cq(struct ib_cq *cq, int
budget, struct ib_wc *poll_wc)
*/
int ib_process_cq_direct(struct ib_cq *cq, int budget)
{
- struct ib_wc wcs[IB_POLL_BATCH];
+ struct ib_wc wcs[IB_POLL_BATCH_DIRECT];

- return __ib_process_cq(cq, budget, wcs);
+ return __ib_process_cq(cq, budget, wcs, IB_POLL_BATCH_DIRECT);
}
EXPORT_SYMBOL(ib_process_cq_direct);

@@ -88,7 +97,7 @@ static int ib_poll_handler(struct irq_poll *iop, int
budget)
struct ib_cq *cq = container_of(iop, struct ib_cq, iop);
int completed;

- completed = __ib_process_cq(cq, budget, NULL);
+ completed = __ib_process_cq(cq, budget, NULL, 0);
if (completed < budget) {
irq_poll_complete(&cq->iop);
if (ib_req_notify_cq(cq, IB_POLL_FLAGS) > 0)
@@ -108,7 +117,7 @@ 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, NULL);
+ completed = __ib_process_cq(cq, IB_POLL_BUDGET_WORKQUEUE, NULL, 0);
if (completed >= IB_POLL_BUDGET_WORKQUEUE ||
ib_req_notify_cq(cq, IB_POLL_FLAGS) > 0)
queue_work(ib_comp_wq, &cq->work);


>
> Jason
>

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