From: John Garry john.garry@huawei.com Sent: Wednesday, October 6, 2021 9:03 AM
On 06/10/2021 16:01, Michael Kelley wrote:
From: John Garry john.garry@huawei.com 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