From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Wei Hu (Xavier)" Subject: Re: [PATCH for-next 05/20] RDMA/hns: Add command queue support for hip08 RoCE driver Date: Tue, 26 Sep 2017 23:24:41 +0800 Message-ID: References: <1504084998-64397-1-git-send-email-xavier.huwei@huawei.com> <1504084998-64397-6-git-send-email-xavier.huwei@huawei.com> <1506359213.120853.75.camel@redhat.com> <20170925171821.GQ25094@mtr-leonro.local> <1506361015.120853.81.camel@redhat.com> <59CA5261.80209@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <59CA5261.80209-hv44wF8Li93QT0dZR+AlfA@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Doug Ledford , Leon Romanovsky Cc: linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, lijun_nudt-9Onoh4P/yGk@public.gmane.org, oulijun-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, charles.chenxin-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, liuyixian-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, xushaobo2-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, zhangxiping3-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, xavier.huwei-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, linuxarm-hv44wF8Li93QT0dZR+AlfA@public.gmane.org List-Id: linux-rdma@vger.kernel.org On 2017/9/26 21:13, Wei Hu (Xavier) wrote: > > > On 2017/9/26 1:36, Doug Ledford wrote: >> On Mon, 2017-09-25 at 20:18 +0300, Leon Romanovsky wrote: >>> On Mon, Sep 25, 2017 at 01:06:53PM -0400, Doug Ledford wrote: >>>> On Wed, 2017-08-30 at 17:23 +0800, Wei Hu (Xavier) wrote: >>>> >>>>> + /* >>>>> + * If the command is sync, wait for the firmware to >>>>> write >>>>> back, >>>>> + * if multi descriptors to be sent, use the first one to >>>>> check >>>>> + */ >>>>> + if ((desc->flag) & HNS_ROCE_CMD_FLAG_NO_INTR) { >>>>> + do { >>>>> + if (hns_roce_cmq_csq_done(hr_dev)) >>>>> + break; >>>>> + usleep_range(1000, 2000); >>>>> + timeout++; >>>>> + } while (timeout < priv->cmq.tx_timeout); >>>>> + } >>>> then we spin here for a maximum amount of time between 200 and >>>> 400ms, >>>> so 1/4 to 1/2 a second. All the time we are holding the bh lock on >>>> this CPU. That seems excessive to me. If we are going to spin >>>> that >>>> long, can you find a way to allocate/reserve your resources, send >>>> the >>>> command, then drop the bh lock while you spin, and retake it before >>>> you >>>> complete once the spinning is done? >>> They don't allocate anything in this loop, but checking the pointers >>> are >>> the same, see hns_roce_cmq_csq_done. >> I'm not sure I understand your intended implication of your comment. I >> wasn't concerned about them allocating anything, only that if the >> hardware is hung, then this loop will hang out for 1/4 to 1/2 a second >> and hold up all bottom half processing on this CPU in the meantime. >> That's the sort of things that provides poor overall system behavior. >> >> Now, since they are really only checking to see if the hardware has >> gotten around to their particular command, and their command is part of >> a ring structure, it's possible to record the original head command, >> and our new head command, and then release the spin_lock_bh around the >> entire do{ }while construct, and in hns_roce_cmd_csq_done() you could >> check that head is not in the range old_head:new_head. That would >> protect you in case something in the bottom half processing queued up >> some more commands and from one sleep to the next the head jumped from >> something other than the new_head to something past new_head, so that >> head == priv->cmq.csq.next_to_use ends up being perpetually false. >> But, that's just from a quick read of the code, I could easily be >> missing something here... > Hi, Doug > Driver issues the cmds in cmq, and firmware gets and processes them. > The firmware process only one cmd at the same time, and it will take > about serveral to 200 us in one cmd currently, so the driver need > not to use stream mode to issue cmd. > > Regards > Wei Hu Hi, Doug We can replace usleep_range(1000, 2000); with the following statement: udelay(1); to avoid spinning too long time and using usleep_range function in spin_lock_bh locked region. Can you give some suggestions? Regards Wei Hu >>>>> +#define HNS_ROCE_CMQ_TX_TIMEOUT 200 >>>> or you could reduce the size of this define... >>>> >>>> -- >>>> Doug Ledford >>>> GPG KeyID: B826A3330E572FDD >>>> Key fingerprint = AE6B 1BDA 122B 23B4 265B 1274 B826 A333 0E57 >>>> 2FDD >>>> >>>> -- >>>> To unsubscribe from this list: send the line "unsubscribe linux- >>>> rdma" in >>>> the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org >>>> More majordomo info at http://vger.kernel.org/majordomo-info.html > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-rdma" in > the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html