On 04/06/2018 04:58 PM, Ming Lei wrote: > On Fri, Apr 06, 2018 at 04:26:49PM +0200, Christian Borntraeger wrote: >> >> >> On 04/06/2018 03:41 PM, Ming Lei wrote: >>> On Fri, Apr 06, 2018 at 12:19:19PM +0200, Christian Borntraeger wrote: >>>> >>>> >>>> On 04/06/2018 11:23 AM, Ming Lei wrote: >>>>> On Fri, Apr 06, 2018 at 10:51:28AM +0200, Christian Borntraeger wrote: >>>>>> >>>>>> >>>>>> On 04/06/2018 10:41 AM, Ming Lei wrote: >>>>>>> On Thu, Apr 05, 2018 at 07:39:56PM +0200, Christian Borntraeger wrote: >>>>>>>> >>>>>>>> >>>>>>>> On 04/05/2018 06:11 PM, Ming Lei wrote: >>>>>>>>>> >>>>>>>>>> Could you please apply the following patch and provide the dmesg boot log? >>>>>>>>> >>>>>>>>> And please post out the 'lscpu' log together from the test machine too. >>>>>>>> >>>>>>>> attached. >>>>>>>> >>>>>>>> As I said before this seems to go way with CONFIG_NR_CPUS=64 or smaller. >>>>>>>> We have 282 nr_cpu_ids here (max 141CPUs on that z13 with SMT2) but only 8 Cores >>>>>>>> == 16 threads. >>>>>>> >>>>>>> OK, thanks! >>>>>>> >>>>>>> The most weird thing is that hctx->next_cpu is computed as 512 since >>>>>>> nr_cpu_id is 282, and hctx->next_cpu should have pointed to one of >>>>>>> possible CPU. >>>>>>> >>>>>>> Looks like it is a s390 specific issue, since I can setup one queue >>>>>>> which has same mapping with yours: >>>>>>> >>>>>>> - nr_cpu_id is 282 >>>>>>> - CPU 0~15 is online >>>>>>> - 64 queues null_blk >>>>>>> - still run all hw queues in .complete handler >>>>>>> >>>>>>> But can't reproduce this issue at all. >>>>>>> >>>>>>> So please test the following patch, which may tell us why hctx->next_cpu >>>>>>> is computed wrong: >>>>>> >>>>>> I see things like >>>>>> >>>>>> [ 8.196907] wrong next_cpu 512, blk_mq_map_swqueue, first_and >>>>>> [ 8.196910] wrong next_cpu 512, blk_mq_map_swqueue, first_and >>>>>> [ 8.196912] wrong next_cpu 512, blk_mq_map_swqueue, first_and >>>>>> [ 8.196913] wrong next_cpu 512, blk_mq_map_swqueue, first_and >>>>>> [ 8.196914] wrong next_cpu 512, blk_mq_map_swqueue, first_and >>>>>> [ 8.196915] wrong next_cpu 512, blk_mq_map_swqueue, first_and >>>>>> [ 8.196916] wrong next_cpu 512, blk_mq_map_swqueue, first_and >>>>>> [ 8.196916] wrong next_cpu 512, blk_mq_map_swqueue, first_and >>>>>> [ 8.196917] wrong next_cpu 512, blk_mq_map_swqueue, first_and >>>>>> [ 8.196918] wrong next_cpu 512, blk_mq_map_swqueue, first_and >>>>>> >>>>>> which is exactly what happens if the find and and operation fails (returns size of bitmap). >>>>> >>>>> Given both 'cpu_online_mask' and 'hctx->cpumask' are shown as correct >>>>> in your previous debug log, it means the following function returns >>>>> totally wrong result on S390. >>>>> >>>>> cpumask_first_and(hctx->cpumask, cpu_online_mask); >>>>> >>>>> The debugfs log shows that each hctx->cpumask includes one online >>>>> CPU(0~15). >>>> >>>> Really? the last log (with the latest patch applied shows a lot of contexts >>>> that do not have CPUs in 0-15: >>>> >>>> e.g. >>>> [ 4.049828] dump CPUs mapped to this hctx: >>>> [ 4.049829] 18 >>>> [ 4.049829] 82 >>>> [ 4.049830] 146 >>>> [ 4.049830] 210 >>>> [ 4.049831] 274 >>> >>> That won't be an issue, since no IO can be submitted from these offline >>> CPUs, then these hctx shouldn't have been run at all. >>> >>> But hctx->next_cpu can be set as 512 for these inactive hctx in >>> blk_mq_map_swqueue(), then please test the attached patch, and if >>> hctx->next_cpu is still set as 512, something is still wrong. >> >> >> WIth this patch I no longer see the "run queue from wrong CPU x, hctx active" messages. >> your debug code still triggers, though. >> >> wrong next_cpu 512, blk_mq_hctx_next_cpu, first_and >> wrong next_cpu 512, blk_mq_hctx_next_cpu, next_and >> >> If we would remove the debug code then dmesg would be clean it seems. > > That is still a bit strange, since for any inactive hctx(without online > CPU mapped), blk_mq_run_hw_queue() will check blk_mq_hctx_has_pending() I think for next_and it is reasonable to see this, as the next_and will return 512 after we have used the last one. In fact the code does call first_and in that case for a reason, no? > first. And there shouldn't be any pending IO for all inactive hctx > in your case, so looks blk_mq_hctx_next_cpu() shouldn't be called for > inactive hctx. > > I will prepare one patchset and post out soon, and hope all these issues > can be covered. > > Thanks, > Ming >
