Hi Kashyap, On Tue, Feb 06, 2018 at 07:57:35PM +0530, Kashyap Desai wrote: > > -----Original Message----- > > From: Ming Lei [mailto:ming.lei@xxxxxxxxxx] > > Sent: Tuesday, February 6, 2018 6:02 PM > > To: Kashyap Desai > > Cc: Hannes Reinecke; Jens Axboe; linux-block@xxxxxxxxxxxxxxx; Christoph > > Hellwig; Mike Snitzer; linux-scsi@xxxxxxxxxxxxxxx; Arun Easi; Omar > Sandoval; > > Martin K . Petersen; James Bottomley; Christoph Hellwig; Don Brace; > Peter > > Rivera; Paolo Bonzini; Laurence Oberman > > Subject: Re: [PATCH 0/5] blk-mq/scsi-mq: support global tags & introduce > > force_blk_mq > > > > Hi Kashyap, > > > > On Tue, Feb 06, 2018 at 04:59:51PM +0530, Kashyap Desai wrote: > > > > -----Original Message----- > > > > From: Ming Lei [mailto:ming.lei@xxxxxxxxxx] > > > > Sent: Tuesday, February 6, 2018 1:35 PM > > > > To: Kashyap Desai > > > > Cc: Hannes Reinecke; Jens Axboe; linux-block@xxxxxxxxxxxxxxx; > > > > Christoph Hellwig; Mike Snitzer; linux-scsi@xxxxxxxxxxxxxxx; Arun > > > > Easi; Omar > > > Sandoval; > > > > Martin K . Petersen; James Bottomley; Christoph Hellwig; Don Brace; > > > Peter > > > > Rivera; Paolo Bonzini; Laurence Oberman > > > > Subject: Re: [PATCH 0/5] blk-mq/scsi-mq: support global tags & > > > > introduce force_blk_mq > > > > > > > > Hi Kashyap, > > > > > > > > On Tue, Feb 06, 2018 at 11:33:50AM +0530, Kashyap Desai wrote: > > > > > > > We still have more than one reply queue ending up completion > > > > > > > one > > > CPU. > > > > > > > > > > > > pci_alloc_irq_vectors(PCI_IRQ_AFFINITY) has to be used, that > > > > > > means smp_affinity_enable has to be set as 1, but seems it is > > > > > > the default > > > > > setting. > > > > > > > > > > > > Please see kernel/irq/affinity.c, especially > > > > > > irq_calc_affinity_vectors() > > > > > which > > > > > > figures out an optimal number of vectors, and the computation is > > > > > > based > > > > > on > > > > > > cpumask_weight(cpu_possible_mask) now. If all offline CPUs are > > > > > > mapped to some of reply queues, these queues won't be active(no > > > > > > request submitted > > > > > to > > > > > > these queues). The mechanism of PCI_IRQ_AFFINITY basically makes > > > > > > sure > > > > > that > > > > > > more than one irq vector won't be handled by one same CPU, and > > > > > > the irq vector spread is done in irq_create_affinity_masks(). > > > > > > > > > > > > > Try to reduce MSI-x vector of megaraid_sas or mpt3sas driver > > > > > > > via module parameter to simulate the issue. We need more > > > > > > > number of Online CPU than reply-queue. > > > > > > > > > > > > IMO, you don't need to simulate the issue, > > > > > > pci_alloc_irq_vectors( > > > > > > PCI_IRQ_AFFINITY) will handle that for you. You can dump the > > > > > > returned > > > > > irq > > > > > > vector number, num_possible_cpus()/num_online_cpus() and each > > > > > > irq vector's affinity assignment. > > > > > > > > > > > > > We may see completion redirected to original CPU because of > > > > > > > "QUEUE_FLAG_SAME_FORCE", but ISR of low level driver can keep > > > > > > > one CPU busy in local ISR routine. > > > > > > > > > > > > Could you dump each irq vector's affinity assignment of your > > > > > > megaraid in > > > > > your > > > > > > test? > > > > > > > > > > To quickly reproduce, I restricted to single MSI-x vector on > > > > > megaraid_sas driver. System has total 16 online CPUs. > > > > > > > > I suggest you don't do the restriction of single MSI-x vector, and > > > > just > > > use the > > > > device supported number of msi-x vector. > > > > > > Hi Ming, CPU lock up is seen even though it is not single msi-x > vector. > > > Actual scenario need some specific topology and server for overnight > test. > > > Issue can be seen on servers which has more than 16 logical CPUs and > > > Thunderbolt series MR controller which supports at max 16 MSIx > vectors. > > > > > > > > > > > > > > Output of affinity hints. > > > > > kernel version: > > > > > Linux rhel7.3 4.15.0-rc1+ #2 SMP Mon Feb 5 12:13:34 EST 2018 > > > > > x86_64 > > > > > x86_64 > > > > > x86_64 GNU/Linux > > > > > PCI name is 83:00.0, dump its irq affinity: > > > > > irq 105, cpu list 0-3,8-11 > > > > > > > > In this case, which CPU is selected for handling the interrupt is > > > decided by > > > > interrupt controller, and it is easy to cause CPU overload if > > > > interrupt > > > controller > > > > always selects one same CPU to handle the irq. > > > > > > > > > > > > > > Affinity mask is created properly, but only CPU-0 is overloaded > > > > > with interrupt processing. > > > > > > > > > > # numactl --hardware > > > > > available: 2 nodes (0-1) > > > > > node 0 cpus: 0 1 2 3 8 9 10 11 > > > > > node 0 size: 47861 MB > > > > > node 0 free: 46516 MB > > > > > node 1 cpus: 4 5 6 7 12 13 14 15 > > > > > node 1 size: 64491 MB > > > > > node 1 free: 62805 MB > > > > > node distances: > > > > > node 0 1 > > > > > 0: 10 21 > > > > > 1: 21 10 > > > > > > > > > > Output of system activities (sar). (gnice is 100% and it is > > > > > consumed in megaraid_sas ISR routine.) > > > > > > > > > > > > > > > 12:44:40 PM CPU %usr %nice %sys %iowait > %steal > > > > > %irq %soft %guest %gnice %idle > > > > > 12:44:41 PM all 6.03 0.00 29.98 0.00 > > > > > 0.00 0.00 0.00 0.00 0.00 > 63.99 > > > > > 12:44:41 PM 0 0.00 0.00 0.00 > 0.00 > > > > > 0.00 0.00 0.00 0.00 100.00 0 > > > > > > > > > > > > > > > In my test, I used rq_affinity is set to 2. > > > > > (QUEUE_FLAG_SAME_FORCE). I also used " host_tagset" V2 patch set > for > > megaraid_sas. > > > > > > > > > > Using RFC requested in - > > > > > "https://marc.info/?l=linux-scsi&m=151601833418346&w=2 " lockup is > > > > > avoided (you can noticed that gnice is shifted to softirq. Even > > > > > though it is 100% consumed, There is always exit for existing > > > > > completion loop due to irqpoll_weight @irq_poll_init(). > > > > > > > > > > Average: CPU %usr %nice %sys %iowait > %steal > > > > > %irq %soft %guest %gnice %idle > > > > > Average: all 4.25 0.00 21.61 0.00 > > > > > 0.00 0.00 6.61 0.00 0.00 67.54 > > > > > Average: 0 0.00 0.00 0.00 > 0.00 > > > > > 0.00 0.00 100.00 0.00 0.00 0.00 > > > > > > > > > > > > > > > Hope this clarifies. We need different fix to avoid lockups. Can > > > > > we consider using irq poll interface if #CPU is more than Reply > > > queue/MSI-x. > > > > > ? > > > > > > > > Please use the device's supported msi-x vectors number, and see if > > > > there > > > is this > > > > issue. If there is, you can use irq poll too, which isn't > > > > contradictory > > > with the > > > > blk-mq approach taken by this patchset. > > > > > > Device supported scenario need more time to reproduce, but it is more > > > quick method is to just use single MSI-x vector and try to create > > > worst case IO completion loop. > > > Using irq poll, my test run without any CPU lockup. I tried your > > > latest V2 series as well and that is also behaving the same. > > > > Again, you can use irq poll, which isn't contradictory with blk-mq. > > Just wanted to explained that issue of CPU lock up is different. Thanks > for clarification. > > > > > > > > BTW - I am seeing drastically performance drop using V2 series of > > > patch on megaraid_sas. Those who is testing HPSA, can also verify if > > > that is a generic behavior. > > > > OK, I will see if I can find a megaraid_sas to see the performance drop > issue. If I > > can't, I will try to run performance test on HPSA. > > Patch is appended. > > > > > Could you share us your patch for enabling global_tags/MQ on > megaraid_sas > > so that I can reproduce your test? > > > > > See below perf top data. "bt_iter" is consuming 4 times more CPU. > > > > Could you share us what the IOPS/CPU utilization effect is after > applying the > > patch V2? And your test script? > Regarding CPU utilization, I need to test one more time. Currently system > is in used. > > I run below fio test on total 24 SSDs expander attached. > > numactl -N 1 fio jbod.fio --rw=randread --iodepth=64 --bs=4k > --ioengine=libaio --rw=randread > > Performance dropped from 1.6 M IOPs to 770K IOPs. > > > > > In theory, it shouldn't, because the HBA only supports HBA wide tags, > that > > means the allocation has to share a HBA wide sbitmap no matter if global > tags > > is used or not. > > > > Anyway, I will take a look at the performance test and data. > > > > > > Thanks, > > Ming > > > Megaraid_sas version of shared tag set. Thanks for providing the patch. > > > diff --git a/drivers/scsi/megaraid/megaraid_sas_base.c > b/drivers/scsi/megaraid/megaraid_sas_base.c > index 0f1d88f..75ea86b 100644 > --- a/drivers/scsi/megaraid/megaraid_sas_base.c > +++ b/drivers/scsi/megaraid/megaraid_sas_base.c > @@ -50,6 +50,7 @@ > #include <linux/mutex.h> > #include <linux/poll.h> > #include <linux/vmalloc.h> > +#include <linux/blk-mq-pci.h> > > #include <scsi/scsi.h> > #include <scsi/scsi_cmnd.h> > @@ -220,6 +221,15 @@ static int megasas_get_ld_vf_affiliation(struct > megasas_instance *instance, > static inline void > megasas_init_ctrl_params(struct megasas_instance *instance); > > + > +static int megaraid_sas_map_queues(struct Scsi_Host *shost) > +{ > + struct megasas_instance *instance; > + instance = (struct megasas_instance *)shost->hostdata; > + > + return blk_mq_pci_map_queues(&shost->tag_set, instance->pdev); > +} > + > /** > * megasas_set_dma_settings - Populate DMA address, length and flags for > DCMDs > * @instance: Adapter soft state > @@ -3177,6 +3187,8 @@ struct device_attribute *megaraid_host_attrs[] = { > .use_clustering = ENABLE_CLUSTERING, > .change_queue_depth = scsi_change_queue_depth, > .no_write_same = 1, > + .map_queues = megaraid_sas_map_queues, > + .host_tagset = 1, > }; > > /** > @@ -5965,6 +5977,9 @@ static int megasas_io_attach(struct megasas_instance > *instance) > host->max_lun = MEGASAS_MAX_LUN; > host->max_cmd_len = 16; > > + /* map reply queue to blk_mq hw queue */ > + host->nr_hw_queues = instance->msix_vectors; > + > /* > * Notify the mid-layer about the new controller > */ > diff --git a/drivers/scsi/megaraid/megaraid_sas_fusion.c > b/drivers/scsi/megaraid/megaraid_sas_fusion.c > index 073ced0..034d976 100644 > --- a/drivers/scsi/megaraid/megaraid_sas_fusion.c > +++ b/drivers/scsi/megaraid/megaraid_sas_fusion.c > @@ -2655,11 +2655,15 @@ static void megasas_stream_detect(struct > megasas_instance *instance, > fp_possible = (io_info.fpOkForIo > 0) ? true : > false; > } > > +#if 0 > /* Use raw_smp_processor_id() for now until cmd->request->cpu is > CPU > id by default, not CPU group id, otherwise all MSI-X queues > won't > be utilized */ > cmd->request_desc->SCSIIO.MSIxIndex = instance->msix_vectors ? > raw_smp_processor_id() % instance->msix_vectors : 0; > +#endif > + > + cmd->request_desc->SCSIIO.MSIxIndex = > blk_mq_unique_tag_to_hwq(scp->request->tag); Looks the above line is wrong, and you just use reply queue 0 in this way to complete rq. Follows the correct usage: cmd->request_desc->SCSIIO.MSIxIndex = blk_mq_unique_tag_to_hwq(blk_mq_unique_tag(scp->request)); > > praid_context = &io_request->RaidContext; > > @@ -2985,9 +2989,13 @@ static void megasas_build_ld_nonrw_fusion(struct > megasas_instance *instance, > } > > cmd->request_desc->SCSIIO.DevHandle = io_request->DevHandle; > + > +#if 0 > cmd->request_desc->SCSIIO.MSIxIndex = > instance->msix_vectors ? > (raw_smp_processor_id() % instance->msix_vectors) : 0; > +#endif > + cmd->request_desc->SCSIIO.MSIxIndex = > blk_mq_unique_tag_to_hwq(scmd->request->tag); Same with above, could you fix the patch and run your performance test again? Thanks Ming
