From mboxrd@z Thu Jan 1 00:00:00 1970 From: Doug Ledford Subject: Re: [PATCH for-next 05/20] RDMA/hns: Add command queue support for hip08 RoCE driver Date: Mon, 25 Sep 2017 13:36:55 -0400 Message-ID: <1506361015.120853.81.camel@redhat.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> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20170925171821.GQ25094-U/DQcQFIOTAAJjI8aNfphQ@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Leon Romanovsky Cc: "Wei Hu (Xavier)" , 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-9Onoh4P/yGk@public.gmane.org, linuxarm-hv44wF8Li93QT0dZR+AlfA@public.gmane.org List-Id: linux-rdma@vger.kernel.org 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... > > > > > +#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 -- 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