Messages in this thread | | | Date | Mon, 3 Apr 2023 01:23:55 -0400 | Subject | Re: [PATCH v3 10/11] scsi: scsi_debug: Only allow sdebug_max_queue be modified when no shosts | From | Douglas Gilbert <> |
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On 2023-03-27 03:43, John Garry wrote: > The shost->can_queue value is initially used to set per-HW queue context > tag depth in the block layer. This ensures that the shost is not sent too > many commands which it can deal with. However lowering sdebug_max_queue > separately means that we can easily overload the shost, as in the following > example: > > $ cat /sys/bus/pseudo/drivers/scsi_debug/max_queue > 192 > $ cat /sys/class/scsi_host/host0/can_queue > 192 > $ echo 100 > /sys/bus/pseudo/drivers/scsi_debug/max_queue > $ cat /sys/class/scsi_host/host0/can_queue > 192 > $ fio --filename=/dev/sda --direct=1 --rw=read --bs=4k --iodepth=256 > --runtime=1200 --numjobs=10 --time_based --group_reporting > --name=iops-test-job --eta-newline=1 --readonly --ioengine=io_uring > --hipri --exitall_on_error > iops-test-job: (g=0): rw=read, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=io_uring, iodepth=256 > ... > fio-3.28 > Starting 10 processes > [ 111.269885] scsi_io_completion_action: 400 callbacks suppressed > [ 111.269885] blk_print_req_error: 400 callbacks suppressed > [ 111.269889] I/O error, dev sda, sector 440 op 0x0:(READ) flags 0x1200000 phys_seg 1 prio class 2 > [ 111.269892] sd 0:0:0:0: [sda] tag#132 FAILED Result: hostbyte=DID_ABORT driverbyte=DRIVER_OK cmd_age=0s > [ 111.269897] sd 0:0:0:0: [sda] tag#132 CDB: Read(10) 28 00 00 00 01 68 00 00 08 00 > [ 111.277058] I/O error, dev sda, sector 360 op 0x0:(READ) flags 0x1200000 phys_seg 1 prio class 2 > > [...] > > Ensure that this cannot happen by allowing sdebug_max_queue be modified > only when we have no shosts. As such, any shost->can_queue value will > match sdebug_max_queue, and sdebug_max_queue cannot be modified separately. > > Since retired_max_queue is no longer set, remove support. > > Continue to apply the restriction that sdebug_host_max_queue cannot be > modified when sdebug_host_max_queue is set. Adding support for that would > mean extra code, and no one has complained about this restriction > previously. > > A command like the following may be used to remove a shost: > echo -1 > /sys/bus/pseudo/drivers/scsi_debug/add_host > > Signed-off-by: John Garry <john.g.garry@oracle.com> Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Thanks.
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