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    SubjectRe: sd_resume redundant? [was: [PATCH] libata: implement ata_wait_after_reset()]
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    On Sun, May 20, 2007 11:54, Tejun Heo wrote:
    > Indan Zupancic wrote:
    >> On Sat, May 19, 2007 21:04, Tejun Heo wrote:
    >>> Tejun Heo wrote:
    >>>> Yeah, if SCR registers are accessible, 0xff doesn't indicate the device
    >>>> isn't there, so the whole skip-0xff logic probably shouldn't apply in
    >>>> such cases, but we can also achieve pretty good result by just making
    >>>> the first reset tries a bit more aggressive.
    >>> So, here's the patch.
    >>>
    >>> Paul, can you please test this patch without the previous patch? Indan,
    >>> this should reduce the resume delay. Please test. But you'll still
    >>> feel some added delay compared to 2.6.20 due to the mentioned
    >>> suspend/resume change.
    >>
    >> This removed the COMRESET errors indeed, and with sd_resume()
    >> disabled everything is speedy again (2s or so. Still a desktop pc).
    >> I didn't try with sd_resume enabled.
    >
    > Can you try to measure with sd_resume in place?

    [ 2.173366] sd 0:0:0:0: [sda] Starting disk
    [ 2.475422] ata2: SATA link down (SStatus 0 SControl 310)
    [ 5.478403] ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
    [ 5.481928] ata1.00: ata_hpa_resize 1: sectors = 234441648, hpa_sectors = 234441648
    [ 5.485904] ata1.00: ata_hpa_resize 1: sectors = 234441648, hpa_sectors = 234441648
    [ 5.485913] ata1.00: configured for UDMA/100
    [ 5.505109] sd 0:0:0:0: [sda] 234441648 512-byte hardware sectors (120034 MB)
    [ 5.505461] sd 0:0:0:0: [sda] Write Protect is off
    [ 5.505465] sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
    [ 5.505612] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or
    FUA
    ...
    [ 6.157259] Restarting tasks ... done.


    And with echo 0 > /sys/class/scsi_disk/0\:0\:0\:0/manage_start_stop:

    [ 2.476476] ata2: SATA link down (SStatus 0 SControl 310)
    ...
    [ 2.825479] Restarting tasks ... done.
    ...
    [ 5.022076] ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
    [ 5.025605] ata1.00: ata_hpa_resize 1: sectors = 234441648, hpa_sectors = 234441648
    [ 5.028594] ata1.00: ata_hpa_resize 1: sectors = 234441648, hpa_sectors = 234441648
    [ 5.028606] ata1.00: configured for UDMA/100
    [ 5.028720] sd 0:0:0:0: [sda] 234441648 512-byte hardware sectors (120034 MB)
    [ 5.028767] sd 0:0:0:0: [sda] Write Protect is off
    [ 5.028773] sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
    [ 5.028831] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or
    FUA

    So over all it takes half a second longer to detect the disk, but because everything waits on it,
    it takes more than three seconds longer to resume.

    Setting manage_start_stop to 0 fixes it and is good enough for me, I didn't notice anything bad yet
    because of the unmanaged stop. Implementing background spin up will fix it too.


    >> Everything seems to work fine without sd_resume(), so why is it needed?
    >
    > Because not all disks spin up without being told to do so and like it or
    > not spinning disks up on resume is the default behavior. As I wrote in
    > the other reply, it would be worthwhile to make it configurable.

    Not even after they receive a read command? Ugh.

    Greeting,

    Indan


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