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: Wed, 27 Sep 2017 00:13:11 +0800 Message-ID: <5514bf6d-3a98-a6fe-ea90-476f5ae1f623@tom.com> 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> <20170926155149.GE6816@mtr-leonro.local> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20170926155149.GE6816-U/DQcQFIOTAAJjI8aNfphQ@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Leon Romanovsky Cc: Doug Ledford , 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, xavier.huwei-WVlzvzqoTvw@public.gmane.org List-Id: linux-rdma@vger.kernel.org On 2017/9/26 23:51, Leon Romanovsky wrote: > On Tue, Sep 26, 2017 at 11:24:41PM +0800, Wei Hu (Xavier) wrote: >> >> 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 som=e suggestions? > He already suggested number of options, while the simple one was to reduce > HNS_ROCE_CMQ_TX_TIMEOUT from 200 to be something sane (for example 5). > > Thanks Thanks, Leon Actually We want to use another option: replace usleep_range(1000, 2000); with the following statement: udelay(1); And if so, we can avoid using usleep_range function in spin_lock_bh spin region, because it probally cause calltrace by rcu. Best regards Wei Hu >> 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