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() 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
