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    SubjectRe: Understanding I/O behaviour - next try

    --- Jens Axboe <jens.axboe@oracle.com> wrote:

    > On Tue, Aug 28 2007, Martin Knoblauch wrote:
    > > Keywords: I/O, bdi-v9, cfs
    > >
    >
    > Try limiting the queue depth on the cciss device, some of those are
    > notoriously bad at starving commands. Something like the below hack,
    > see
    > if it makes a difference (and please verify in dmesg that it prints
    > the
    > message about limiting depth!):
    >
    > diff --git a/drivers/block/cciss.c b/drivers/block/cciss.c
    > index 084358a..257e1c3 100644
    > --- a/drivers/block/cciss.c
    > +++ b/drivers/block/cciss.c
    > @@ -2992,7 +2992,12 @@ static int cciss_pci_init(ctlr_info_t *c,
    > struct pci_dev *pdev)
    > if (board_id == products[i].board_id) {
    > c->product_name = products[i].product_name;
    > c->access = *(products[i].access);
    > +#if 0
    > c->nr_cmds = products[i].nr_cmds;
    > +#else
    > + c->nr_cmds = 2;
    > + printk("cciss: limited max commands to 2\n");
    > +#endif
    > break;
    > }
    > }
    >
    > --
    > Jens Axboe
    >
    >
    >
    Hi Jens,

    thanks for the suggestion. Unfortunatelly the non-direct [parallel]
    writes to the device got considreably slower. I guess the "6i"
    controller copes better with higher values.

    Can nr_cmds be changed at runtime? Maybe there is a optimal setting.

    [ 69.438851] SCSI subsystem initialized
    [ 69.442712] HP CISS Driver (v 3.6.14)
    [ 69.442871] ACPI: PCI Interrupt 0000:04:03.0[A] -> GSI 51 (level,
    low) -> IRQ 51
    [ 69.442899] cciss: limited max commands to 2 (Smart Array 6i)
    [ 69.482370] cciss0: <0x46> at PCI 0000:04:03.0 IRQ 51 using DAC
    [ 69.494352] blocks= 426759840 block_size= 512
    [ 69.498350] heads=255, sectors=32, cylinders=52299
    [ 69.498352]
    [ 69.498509] blocks= 426759840 block_size= 512
    [ 69.498602] heads=255, sectors=32, cylinders=52299
    [ 69.498604]
    [ 69.498608] cciss/c0d0: p1 p2

    Cheers
    Martin

    ------------------------------------------------------
    Martin Knoblauch
    email: k n o b i AT knobisoft DOT de
    www: http://www.knobisoft.de
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