On Fri, Apr 06, 2018 at 05:11:53PM +0200, Christian Borntraeger wrote: > > > 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? It is possible for dumping 'first_and' when there isn't any online CPUs mapped to this hctx. But my question is that for this case, there shouldn't be any IO queued for this hctx, and blk_mq_hctx_has_pending() has been called to check that, so blk_mq_hctx_next_cpu() should have only be called when blk_mq_hctx_has_pending() in blk_mq_run_hw_queue() is true. Thanks, Ming
