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    Subject[PATCH] aic94xx: Increase can_queue and cmds_per_lun
    Hi all,

    Below is a patch that sets cmd_per_lun and can_queue in the aic94xx
    driver's scsi_host_template to better performing values than what's
    there currently. The cmd_per_lun setting is stolen straight out of the
    adp94xx source, and can_queue is derived from the max_scb value that we
    calculate in asd_init_hw. To the best of my (admittedly limited)
    knowledge, this method provides the correct values (can_queue = 443 in
    both adp94xx and aic94xx on my 9405W) but if anybody knows better,
    please enlighten me. :)

    That said, the effect of leaving these values set to 1 is terrible
    performance in the case of either (a) certain Maxtor SAS drives flying
    solo or (b) flooding several disks with I/O simultaneously (md-raid).
    There may be more scenarios where we see similar problems that I
    haven't uncovered.

    Just for grins, I ran bogodisk (an O_DIRECT-enabled read speed test)
    against three different scenarios:

    1) adp94xx 1.0.8-6, pounded into 2.6.18-rc4 [green]
    2) aic94xx 1.0.2, without this patch [red]
    3) aic94xx 1.0.2, with this [blue]

    ...with these results:

    http://sweaglesw.net/~djwong/programs/bogodisk/bd_graphs/bad_sas.0.png

    As you can see, the read performance is cut in half by the aic94xx
    driver not getting a chance to have multiple I/Os in flight at any given
    time. With the patch, the two drivers are fairly close bandwidth-wise.
    Also thanks to Mike Anderson for helping me figure this out.

    --D

    Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>

    diff --git a/drivers/scsi/aic94xx/aic94xx_hwi.h b/drivers/scsi/aic94xx/aic94xx_hwi.h
    index c7d5053..a2d8881 100644
    --- a/drivers/scsi/aic94xx/aic94xx_hwi.h
    +++ b/drivers/scsi/aic94xx/aic94xx_hwi.h
    @@ -36,6 +36,9 @@
    #include "aic94xx.h"
    #include "aic94xx_sas.h"

    +/* Leave a few empty data buffers. */
    +#define ASD_FREE_SCBS 3
    +
    /* Define ASD_MAX_PHYS to the maximum phys ever. Currently 8. */
    #define ASD_MAX_PHYS 8
    #define ASD_PCBA_SN_SIZE 12
    diff --git a/drivers/scsi/aic94xx/aic94xx_init.c b/drivers/scsi/aic94xx/aic94xx_init.c
    index 3ec2e46..34a7b4b 100644
    --- a/drivers/scsi/aic94xx/aic94xx_init.c
    +++ b/drivers/scsi/aic94xx/aic94xx_init.c
    @@ -71,7 +72,7 @@ static struct scsi_host_template aic94xx
    .change_queue_type = sas_change_queue_type,
    .bios_param = sas_bios_param,
    .can_queue = 1,
    - .cmd_per_lun = 1,
    + .cmd_per_lun = 2,
    .this_id = -1,
    .sg_tablesize = SG_ALL,
    .max_sectors = SCSI_DEFAULT_MAX_SECTORS,
    @@ -612,13 +616,17 @@ static int __devinit asd_pci_probe(struc
    goto Err_free_cache;

    asd_printk("device %s: SAS addr %llx, PCBA SN %s, %d phys, %d enabled "
    - "phys, flash %s, BIOS %s%d\n",
    + "phys, flash %s, BIOS %s%d, SCBs %d\n",
    pci_name(dev), SAS_ADDR(asd_ha->hw_prof.sas_addr),
    asd_ha->hw_prof.pcba_sn, asd_ha->hw_prof.max_phys,
    asd_ha->hw_prof.num_phys,
    asd_ha->hw_prof.flash.present ? "present" : "not present",
    asd_ha->hw_prof.bios.present ? "build " : "not present",
    - asd_ha->hw_prof.bios.bld);
    + asd_ha->hw_prof.bios.bld,
    + asd_ha->hw_prof.max_scbs);
    +
    + aic94xx_sht.can_queue = asd_ha->hw_prof.max_scbs - ASD_FREE_SCBS;
    + shost->can_queue = aic94xx_sht.can_queue;

    if (use_msi)
    pci_enable_msi(asd_ha->pcidev);
    -
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