Re: [PATCH AUTOSEL for 4.14 039/161] IB/cq: Don't force IB_POLL_DIRECT poll context for ib_process_cq_direct

[Sasha Levin <Alexander.Levin@microsoft.com>]

Grabbed it for both 4.14 and 4.15, thanks Max!

On Mon, Apr 09, 2018 at 07:21:29PM +0300, Max Gurtovoy wrote:
>Hi Sasha,
>please consider taking a small fix for this one (also useful for 4.15):
>
>commit d3b9e8ad425cfd5b9116732e057f1b48e4d3bcb8
>Author: Max Gurtovoy <maxg@mellanox.com>
>Date:   Mon Mar 5 20:09:48 2018 +0200
>
>    RDMA/core: Reduce poll batch for direct cq polling
>
>    Fix warning limit for kernel stack consumption:
>
>    drivers/infiniband/core/cq.c: In function 'ib_process_cq_direct':
>    drivers/infiniband/core/cq.c:78:1: error: the frame size of 1032 bytes
>    is larger than 1024 bytes [-Werror=frame-larger-than=]
>
>    Using smaller ib_wc array on the stack brings us comfortably below that
>    limit again.
>
>    Fixes: 246d8b184c10 ("IB/cq: Don't force IB_POLL_DIRECT poll 
>context for ib_process_cq_direct")
>    Reported-by: Arnd Bergmann <arnd@arndb.de>
>    Reviewed-by: Sergey Gorenko <sergeygo@mellanox.com>
>    Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
>    Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
>    Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
>    Acked-by: Arnd Bergmann <arnd@arndb.de>
>    Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
>
>
>-Max.
>
>
>On 4/9/2018 3:20 AM, Sasha Levin wrote:
>>From: Sagi Grimberg <sagi@grimberg.me>
>>
>>[ Upstream commit 246d8b184c100e8eb6b4e8c88f232c2ed2a4e672 ]
>>
>>polling the completion queue directly does not interfere
>>with the existing polling logic, hence drop the requirement.
>>Be aware that running ib_process_cq_direct with non IB_POLL_DIRECT
>>CQ may trigger concurrent CQ processing.
>>
>>This can be used for polling mode ULPs.
>>
>>Cc: Bart Van Assche <bart.vanassche@wdc.com>
>>Reported-by: Steve Wise <swise@opengridcomputing.com>
>>Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
>>[maxg: added wcs array argument to __ib_process_cq]
>>Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
>>Signed-off-by: Doug Ledford <dledford@redhat.com>
>>Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
>>---
>>  drivers/infiniband/core/cq.c | 23 +++++++++++++----------
>>  1 file changed, 13 insertions(+), 10 deletions(-)
>>
>>diff --git a/drivers/infiniband/core/cq.c b/drivers/infiniband/core/cq.c
>>index f2ae75fa3128..c8c5a5a7f433 100644
>>--- a/drivers/infiniband/core/cq.c
>>+++ b/drivers/infiniband/core/cq.c
>>@@ -25,9 +25,10 @@
>>  #define IB_POLL_FLAGS \
>>  	(IB_CQ_NEXT_COMP | IB_CQ_REPORT_MISSED_EVENTS)
>>-static int __ib_process_cq(struct ib_cq *cq, int budget)
>>+static int __ib_process_cq(struct ib_cq *cq, int budget, struct ib_wc *poll_wc)
>>  {
>>  	int i, n, completed = 0;
>>+	struct ib_wc *wcs = poll_wc ? : cq->wc;
>>  	/*
>>  	 * budget might be (-1) if the caller does not
>>@@ -35,9 +36,9 @@ static int __ib_process_cq(struct ib_cq *cq, int budget)
>>  	 * minimum here.
>>  	 */
>>  	while ((n = ib_poll_cq(cq, min_t(u32, IB_POLL_BATCH,
>>-			budget - completed), cq->wc)) > 0) {
>>+			budget - completed), wcs)) > 0) {
>>  		for (i = 0; i < n; i++) {
>>-			struct ib_wc *wc = &cq->wc[i];
>>+			struct ib_wc *wc = &wcs[i];
>>  			if (wc->wr_cqe)
>>  				wc->wr_cqe->done(cq, wc);
>>@@ -60,18 +61,20 @@ static int __ib_process_cq(struct ib_cq *cq, int budget)
>>   * @cq:		CQ to process
>>   * @budget:	number of CQEs to poll for
>>   *
>>- * This function is used to process all outstanding CQ entries on a
>>- * %IB_POLL_DIRECT CQ.  It does not offload CQ processing to a different
>>- * context and does not ask for completion interrupts from the HCA.
>>+ * This function is used to process all outstanding CQ entries.
>>+ * It does not offload CQ processing to a different context and does
>>+ * not ask for completion interrupts from the HCA.
>>+ * Using direct processing on CQ with non IB_POLL_DIRECT type may trigger
>>+ * concurrent processing.
>>   *
>>   * Note: do not pass -1 as %budget unless it is guaranteed that the number
>>   * of completions that will be processed is small.
>>   */
>>  int ib_process_cq_direct(struct ib_cq *cq, int budget)
>>  {
>>-	WARN_ON_ONCE(cq->poll_ctx != IB_POLL_DIRECT);
>>+	struct ib_wc wcs[IB_POLL_BATCH];
>>-	return __ib_process_cq(cq, budget);
>>+	return __ib_process_cq(cq, budget, wcs);
>>  }
>>  EXPORT_SYMBOL(ib_process_cq_direct);
>>@@ -85,7 +88,7 @@ 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);
>>+	completed = __ib_process_cq(cq, budget, NULL);
>>  	if (completed < budget) {
>>  		irq_poll_complete(&cq->iop);
>>  		if (ib_req_notify_cq(cq, IB_POLL_FLAGS) > 0)
>>@@ -105,7 +108,7 @@ 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);
>>+	completed = __ib_process_cq(cq, IB_POLL_BUDGET_WORKQUEUE, NULL);
>>  	if (completed >= IB_POLL_BUDGET_WORKQUEUE ||
>>  	    ib_req_notify_cq(cq, IB_POLL_FLAGS) > 0)
>>  		queue_work(ib_comp_wq, &cq->work);
>>