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Re: Increased memory usage with scsi-mq

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On Mon, Aug 07, 2017 at 02:11:39PM +0200, Paolo Bonzini wrote:
> You could also add a module parameter to the driver, and set it to 64 on
> the kernel command line (there is an example in
> drivers/scsi/vmw_pvscsi.c of how to do it).

[Proviso: I've not tested the performance of difference values, nor do
I have any particular knowledge in this area]

can_queue is documented as:

         * This determines if we will use a non-interrupt driven
         * or an interrupt driven scheme.  It is set to the maximum number
         * of simultaneous commands a given host adapter will accept.

Wouldn't it be better to make it default to k * number of CPUs for
some small integer k?

I looked at the other scsi drivers and they set it to all kinds of
values.  1, small integers, large integers, configurable values.

Also I noticed this code in virtio_scsi.c:

        cmd_per_lun = virtscsi_config_get(vdev, cmd_per_lun) ?: 1;
        shost->cmd_per_lun = min_t(u32, cmd_per_lun, shost->can_queue);

but setting cmd_per_lun (as a qemu virtio-scsi-pci parameter) didn't
seem to make any difference to memory usage.

Rich.

-- 
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Thread

Increased memory usage with scsi-mq "Richard W.M. Jones" <rjones@redhat.com> - 2017-08-04 23:10 +0200
  Re: Increased memory usage with scsi-mq Christoph Hellwig <hch@lst.de> - 2017-08-05 10:50 +0200
    Re: Increased memory usage with scsi-mq "Richard W.M. Jones" <rjones@redhat.com> - 2017-08-05 11:30 +0200
      Re: Increased memory usage with scsi-mq Christoph Hellwig <hch@lst.de> - 2017-08-05 15:50 +0200
        Re: Increased memory usage with scsi-mq "Richard W.M. Jones" <rjones@redhat.com> - 2017-08-05 18:00 +0200
          Re: Increased memory usage with scsi-mq Paolo Bonzini <pbonzini@redhat.com> - 2017-08-07 14:20 +0200
            Re: Increased memory usage with scsi-mq "Richard W.M. Jones" <rjones@redhat.com> - 2017-08-07 14:30 +0200
              Re: Increased memory usage with scsi-mq Paolo Bonzini <pbonzini@redhat.com> - 2017-08-07 15:10 +0200
                Re: Increased memory usage with scsi-mq Christoph Hellwig <hch@lst.de> - 2017-08-09 18:10 +0200
                Re: Increased memory usage with scsi-mq Paolo Bonzini <pbonzini@redhat.com> - 2017-08-09 19:00 +0200
                Re: Increased memory usage with scsi-mq "Richard W.M. Jones" <rjones@redhat.com> - 2017-08-10 14:30 +0200
                Re: Increased memory usage with scsi-mq Paolo Bonzini <pbonzini@redhat.com> - 2017-08-10 15:00 +0200
                Re: Increased memory usage with scsi-mq "Richard W.M. Jones" <rjones@redhat.com> - 2017-08-10 16:20 +0200
                Re: Increased memory usage with scsi-mq Paolo Bonzini <pbonzini@redhat.com> - 2017-08-10 16:40 +0200
                Re: Increased memory usage with scsi-mq "Richard W.M. Jones" <rjones@redhat.com> - 2017-08-10 17:50 +0200
                Re: Increased memory usage with scsi-mq Paolo Bonzini <pbonzini@redhat.com> - 2017-08-10 18:10 +0200

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