linux-kernel - Re: Increased memory usage with scsi-mq

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 7 Aug 2017 13:27:02 +0100
From:   "Richard W.M. Jones" <rjones@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Christoph Hellwig <hch@....de>, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: Increased memory usage with scsi-mq

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.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine.  Supports Linux and Windows.
http://people.redhat.com/~rjones/virt-df/