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

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Date:   Mon, 9 Apr 2018 19:21:29 +0300
From:   Max Gurtovoy <maxg@...lanox.com>
To:     Sasha Levin <Alexander.Levin@...rosoft.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Sagi Grimberg <sagi@...mberg.me>,
        Bart Van Assche <bart.vanassche@....com>,
        Doug Ledford <dledford@...hat.com>
Subject: Re: [PATCH AUTOSEL for 4.14 039/161] IB/cq: Don't force
 IB_POLL_DIRECT poll context for ib_process_cq_direct

Hi Sasha,
please consider taking a small fix for this one (also useful for 4.15):

commit d3b9e8ad425cfd5b9116732e057f1b48e4d3bcb8
Author: Max Gurtovoy <maxg@...lanox.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@...db.de>
     Reviewed-by: Sergey Gorenko <sergeygo@...lanox.com>
     Signed-off-by: Max Gurtovoy <maxg@...lanox.com>
     Signed-off-by: Leon Romanovsky <leonro@...lanox.com>
     Reviewed-by: Bart Van Assche <bart.vanassche@....com>
     Acked-by: Arnd Bergmann <arnd@...db.de>
     Signed-off-by: Jason Gunthorpe <jgg@...lanox.com>


-Max.


On 4/9/2018 3:20 AM, Sasha Levin wrote:
> From: Sagi Grimberg <sagi@...mberg.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@....com>
> Reported-by: Steve Wise <swise@...ngridcomputing.com>
> Signed-off-by: Sagi Grimberg <sagi@...mberg.me>
> [maxg: added wcs array argument to __ib_process_cq]
> Signed-off-by: Max Gurtovoy <maxg@...lanox.com>
> Signed-off-by: Doug Ledford <dledford@...hat.com>
> Signed-off-by: Sasha Levin <alexander.levin@...rosoft.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);
>