From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH] SCSI: don't get target/host busy_count in scsi_mq_get_budget() To: Laurence Oberman , Bart Van Assche , "ming.lei@redhat.com" Cc: "linux-block@vger.kernel.org" , "hch@infradead.org" , "martin.petersen@oracle.com" , "linux-scsi@vger.kernel.org" , "john.garry@huawei.com" , "osandov@fb.com" , "jejb@linux.vnet.ibm.com" References: <20171104015534.32684-1-ming.lei@redhat.com> <1509997522.2409.58.camel@wdc.com> <20171107021125.GB15090@ming.t460p> <1510071607.2656.17.camel@wdc.com> <20171108003934.GB20599@ming.t460p> <26ee805b-883f-d588-5649-13700244b6e8@kernel.dk> <20171108025830.GA30129@ming.t460p> <1a153ff3-9d53-d347-cb16-b8480e690221@kernel.dk> <1510159293.24237.19.camel@wdc.com> <1510165336.13896.1.camel@redhat.com> From: Jens Axboe Message-ID: <80b7a49f-7612-6d27-89e5-bb2f2f27f0d5@kernel.dk> Date: Wed, 8 Nov 2017 11:28:55 -0700 MIME-Version: 1.0 In-Reply-To: <1510165336.13896.1.camel@redhat.com> Content-Type: text/plain; charset=utf-8 List-ID: On 11/08/2017 11:22 AM, Laurence Oberman wrote: > On Wed, 2017-11-08 at 10:57 -0700, Jens Axboe wrote: >> On 11/08/2017 09:41 AM, Bart Van Assche wrote: >>> On Tue, 2017-11-07 at 20:06 -0700, Jens Axboe wrote: >>>> At this point, I have no idea what Bart's setup looks like. Bart, >>>> it >>>> would be REALLY helpful if you could tell us how you are >>>> reproducing >>>> your hang. I don't know why this has to be dragged out. >>> >>> Hello Jens, >>> >>> It is a disappointment to me that you have allowed Ming to evaluate >>> other >>> approaches than reverting "blk-mq: don't handle TAG_SHARED in >>> restart". That >>> patch namely replaces an algorithm that is trusted by the community >>> with an >>> algorithm of which even Ming acknowledged that it is racy. A quote >>> from [1]: >>> "IO hang may be caused if all requests are completed just before >>> the current >>> SCSI device is added to shost->starved_list". I don't know of any >>> way to fix >>> that race other than serializing request submission and completion >>> by adding >>> locking around these actions, which is something we don't want. >>> Hence my >>> request to revert that patch. >> >> I was reluctant to revert it, in case we could work out a better way >> of >> doing it. As I mentioned in the other replies, it's not exactly the >> prettiest or most efficient. However, since we currently don't have >> a good solution for the issue, I'm fine with reverting that patch. >> >>> Regarding the test I run, here is a summary of what I mentioned in >>> previous >>> e-mails: >>> * I modified the SRP initiator such that the SCSI target queue >>> depth is >>>   reduced to one by setting starget->can_queue to 1 from inside >>>   scsi_host_template.target_alloc. >>> * With that modified SRP initiator I run the srp-test software as >>> follows >>>   until something breaks: >>>   while ./run_tests -f xfs -d -e deadline -r 60; do :; done >> >> What kernel options are needed? Where do I download everything I >> need? >> >> In other words, would it be possible to do a fuller guide for getting >> this setup and running? >> >> I'll run my simple test case as well, since it's currently breaking >> basically everywhere. >> >>> Today a system with at least one InfiniBand HCA is required to run >>> that test. >>> When I have the time I will post the SRP initiator and target >>> patches on the >>> linux-rdma mailing list that make it possible to run that test >>> against the >>> SoftRoCE driver (drivers/infiniband/sw/rxe). The only hardware >>> required to >>> use that driver is an Ethernet adapter. >> >> OK, I guess I can't run it then... I'll have to rely on your testing. > > Hello > > I agree with Bart in this case, we should revert this. > My test-bed is tied up and I have not been able to give it back to Ming > so he could follow up on Bart's last update. > > Right now its safer to revert. I had already reverted it when sending out that email, so we should be all set (hopefully). -- Jens Axboe