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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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