From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754689AbeBUPKy (ORCPT ); Wed, 21 Feb 2018 10:10:54 -0500 Received: from userp2130.oracle.com ([156.151.31.86]:38172 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751800AbeBUPKv (ORCPT ); Wed, 21 Feb 2018 10:10:51 -0500 Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 11.2 \(3445.5.20\)) Subject: Re: [PATCH] RDMA/core: reduce IB_POLL_BATCH constant From: Chuck Lever In-Reply-To: Date: Wed, 21 Feb 2018 10:10:27 -0500 Cc: Bart Van Assche , "jgg@ziepe.ca" , "arnd@arndb.de" , "dledford@redhat.com" , "linux-kernel@vger.kernel.org" , "leonro@mellanox.com" , "linux-rdma@vger.kernel.org" Message-Id: <361D2F0F-F03C-438D-9C90-D6ABD0CAC12B@oracle.com> References: <20180220205924.2035765-1-arnd@arndb.de> <1519161268.3737.12.camel@wdc.com> To: Sagi Grimberg X-Mailer: Apple Mail (2.3445.5.20) X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8810 signatures=668675 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=925 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1711220000 definitions=main-1802210184 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id w1LFBEx0017319 > On Feb 21, 2018, at 8:44 AM, Sagi Grimberg wrote: > > >>> On Tue, 2018-02-20 at 21:59 +0100, Arnd Bergmann wrote: >>>> /* # of WCs to poll for with a single call to ib_poll_cq */ >>>> -#define IB_POLL_BATCH 16 >>>> +#define IB_POLL_BATCH 8 >>> >>> The purpose of batch polling is to minimize contention on the cq spinlock. >>> Reducing the IB_POLL_BATCH constant may affect performance negatively. Has >>> the performance impact of this change been verified for all affected drivers >>> (ib_srp, ib_srpt, ib_iser, ib_isert, NVMeOF, NVMeOF target, SMB Direct, NFS >>> over RDMA, ...)? >> Only the users of the DIRECT polling method use an on-stack >> array of ib_wc's. This is only the SRP drivers. >> The other two modes have use of a dynamically allocated array >> of ib_wc's that hangs off the ib_cq. These shouldn't need any >> reduction in the size of this array, and they are the common >> case. >> IMO a better solution would be to change ib_process_cq_direct >> to use a smaller on-stack array, and leave IB_POLL_BATCH alone. > > 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? Agreed, I prefer that all three modes use dynamically allocated memory for that array. > -- > diff --git a/drivers/infiniband/core/cq.c b/drivers/infiniband/core/cq.c > index bc79ca8215d7..cd3e9e124834 100644 > --- a/drivers/infiniband/core/cq.c > +++ b/drivers/infiniband/core/cq.c > @@ -25,10 +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, struct ib_wc *poll_wc) > +static int __ib_process_cq(struct ib_cq *cq, int budget) > { > int i, n, completed = 0; > - struct ib_wc *wcs = poll_wc ? : cq->wc; > + struct ib_wc *wcs = cq->wc; > > /* > * budget might be (-1) if the caller does not > @@ -72,9 +72,9 @@ 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]; > - > - return __ib_process_cq(cq, budget, wcs); > + if (unlikely(WARN_ON_ONCE(!cq->wc))) > + return 0; > + return __ib_process_cq(cq, budget); > } > EXPORT_SYMBOL(ib_process_cq_direct); > > @@ -88,7 +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, NULL); > + completed = __ib_process_cq(cq, budget); > if (completed < budget) { > irq_poll_complete(&cq->iop); > if (ib_req_notify_cq(cq, IB_POLL_FLAGS) > 0) > @@ -108,7 +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, NULL); > + 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); > -- -- Chuck Lever