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? I don't understand what you mean by "so the driver need not to use stream mode to issue cmd". >     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 > > -- Doug Ledford GPG Key ID: B826A3330E572FDD Key fingerprint = AE6B 1BDA 122B 23B4 265B 1274 B826 A333 0E57 2FDD