From: John Garry <john.garry@xxxxxxxxxx> Sent: Wednesday, October 6, 2021 9:03 AM > > On 06/10/2021 16:01, Michael Kelley wrote: > > From: John Garry <john.garry@xxxxxxxxxx> Sent: Wednesday, October 6, 2021 1:17 AM > >> > >> On 06/10/2021 08:03, Dexuan Cui wrote: > >>> After commit ea2f0f77538c, a 416-CPU VM running on Hyper-V hangs during > >>> boot because scsi_add_host_with_dma() sets shost->cmd_per_lun to a > >>> negative number: > >>> 'max_outstanding_req_per_channel' is 352, > >>> 'max_sub_channels' is (416 - 1) / 4 = 103, so in storvsc_probe(), > >>> scsi_driver.can_queue = 352 * (103 + 1) * (100 - 10) / 100 = 32947, which > >>> is bigger than SHRT_MAX (i.e. 32767). > >> > >> Out of curiosity, are these values realistic? You're capping can_queue > >> just because of a data size issue, so, if these values are realistic, > >> seems a weak reason. > >> > > > > The calculated value of can_queue is not realistic. The blk-mq layer > > caps the number of tags at 10240, > > nit: 1024, I think I was thinking about BLK_MQ_MAX_DEPTH (#define'd as 10240), which is used to limit the tag set size in blk_mq_alloc_tag_set(). When running on large VMs on Hyper-V, we can see the "blk-mq: reduced tag depth to 10240" message. :-( Michael
