Messages in this thread | | | Subject | Re: [PATCH for-next 05/20] RDMA/hns: Add command queue support for hip08 RoCE driver | From | "Wei Hu (Xavier)" <> | Date | Wed, 27 Sep 2017 10:46:40 +0800 |
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On 2017/9/27 0:18, Doug Ledford wrote: > On 9/26/2017 9:13 AM, 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. > I'm not sure I understand your response here. > > I get that the driver issues cmds in the cmq, and that the firmware gets > them and processes them. > > I get that the firmware will only work on one command at a time and only > move to the next one once the current one is complete. > > I get that commands take anywhere from a few usec to a couple hundred usec. > > I also get that because you are sleeping for somewhere in between 1000 > and 2000 usecs, that the driver could easily finish a whole slew of > commands. It could do 10 slow commands, or 100 or more fast commands. > What this tells me is that the only reason your current implementation > of hns_roce_cmq_csq_done() works at all is because you keep the device > locked out from any other commands being put on the queue. As far as I > can tell, that's the only way you can guarantee that at some point you > will wake up and the head pointer will be exactly at csq->next_to_use. > Otherwise, if you didn't block them out, then you could sleep with the > head pointer before csq->next_to_use and wake up the next time with it > already well past csq->next_to_use. Am I right about that? While you > are waiting on this command queue, any other commands are blocked from > being placed on the command queue? Hi, Doug, you are right. And one "hns_x" ib device only has one command queue in hip08, other commands will be blocked when waiting on the command queue. > > I don't understand what you mean by "so the driver need not to use > stream mode to issue cmd". Sorry, my expression error. stream -> pipeline
And if you argee, after this patchset has been accepted we will send a following up patch : In hns_roce_cmq_send function, 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.
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 <dledford@redhat.com> >>>>> 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@vger.kernel.org >>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html >> >
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