Recent concurrency improvements in the AHCI driver and CAM need testing

[Sepherosa Ziehau]

On Mon, Apr 11, 2011 at 2:39 PM, Naoya Sugioka <naoya.sugioka at gmail.com> wrote:
> correction :)
>  io_acpi  => io_apic

On the latest master in loader prompt:
set debug.acpi.disabled="pci pci_link pcib"

See whether the timeout still happens.


But I do observed some ahci CMD timeout in VirtualBox 3.2.12 after
recent ahci changes:

ahci0.0: CMD TIMEOUT state=5 slot=18
        cmd-reg 0xdf17<CR,FR,FRE,POD,SUD,ST>
        sactive=00040000 active=00000000 expired=00000000
           sact=00000000     ci=00000000
            STS=50
ahci0.0: disk_rw: timeout
(da0:ahci0:0:0:0): Command timed out
(da0:ahci0:0:0:0): Retrying Command
ahci0.0: CMD TIMEOUT state=5 slot=18
        cmd-reg 0xdf17<CR,FR,FRE,POD,SUD,ST>
        sactive=00040000 active=00000000 expired=00000000
           sact=00000000     ci=00000000
            STS=50
ahci0.0: disk_rw: timeout
(da0:ahci0:0:0:0): Command timed out
(da0:ahci0:0:0:0): Retrying Command

Though it does not seem to affect anything else.

Best Regards,
sephe

>
> On Sun, Apr 10, 2011 at 11:37 PM, Naoya Sugioka <naoya.sugioka at gmail.com> wrote:
>> Hello,
>>
>> This is happened before your recent update, but my laptop showing
>> CMD=15; timeout
>> on ahci0.1 when io_acpi is enabled.  This timeout prevents to complete
>> bootstrap process.
>> I just wonder this is happened because ahci.0.1 is associated to ATAPI
>> (DVD-RW) drive without
>> occupant.
>>
>> dmesg telles:
>> ahci0.1: Found ATAPI "TSSTcorp DVD+/-RW TS-U633F D200" serial="R3476GSSA81272"
>> ahci0.1: tags=0/32 satacap=0202 satafea=0068 NCQ=NO capacity=1.00MB
>> ahci0.1: f85=0000 f86=0000 f87=4000 WC=notsupp RA=notsupp SEC=notsupp
>>
>> then start showing a timeout message.
>>
>> Let me know if you need further information, thank you.
>> -Naoya
>>
>> On Sat, Apr 9, 2011 at 9:00 PM, Matthew Dillon
>> <dillon at apollo.backplane.com> wrote:
>>>    I've pushed some serious changes to the AHCI SATA driver and CAM.
>>>
>>>    One fixes issues where the tags were not being utilized to their fullest
>>>    extent... well, really they weren't being utilized at all.  I'm not
>>>    sure how I missed the problem before, but it is fixed now.
>>>
>>>    The second ensures that read requests cannot saturate all available
>>>    tags and cause writes to stall, and vise-versa, and also separates
>>>    out the read and write BIO streams and treats them as separate entities,
>>>    which means that reads can continue to be dispatched even if writes
>>>    saturate the drive's cache and writes can continue to be dispatched
>>>    even if concurrent read(s) would otherwise eat all available tags.
>>>
>>>    The reason the read/write saturation fixes are important is because
>>>    writes are usually completed instantly since they just go to the drive
>>>    cache, so even if reads are saturated there's no reason not to push
>>>    writes to the drive.  Plus when the HD's cache becomes saturated writes
>>>    no longer complete instantly and would prevent reads from being
>>>    dispatched if all the tags were used to hold the writes.
>>>
>>>    --
>>>
>>>    With these fixes I am getting much better numbers with concurrency
>>>    tests:
>>>
>>>    I now get around 37000 IOPS doing random 512-byte sector reads with
>>>    a Crucial C300 SSD, verses ~8000 or so before the fix.
>>>
>>>    And I now get around ~365 IOPS with the same test on a hard drive,
>>>    verses ~150 IOPS before (remember these are random reads!).
>>>
>>>    blogbench also appears to have much better write/read parallelism
>>>    against the swapcache with the SSD/HD combo.  Memory caches blow
>>>    out at around blog #1300 on my test boxes.
>>>
>>>        With the changes blogbench write performance is maintained through
>>>        blog #1600 or so, without the changes it drops off at #1300.
>>>
>>>        With the changes the swapcache SSD is pushing ~1400 IOPS or so
>>>        satisfying random read requests.  Without the changes the swapcache
>>>        SSD is only pushing ~130 IOPS.
>>>
>>>        With the changes blogbench is able to maintain a ~60000 article
>>>        read rate at the end of the test.  Without the changes the
>>>        read rate is more around ~10000 at the end of the test.  At this
>>>        stage swapcache has cached a significant chunk of the data
>>>        in the SSD so the I/O activity is mixed random SSD and HD reads.
>>>
>>>    --
>>>
>>>    Ok, so I feel a bit sheepish that I missed the fact that the AHCI
>>>    driver wasn't utilizing its tags properly before.  The difference
>>>    in performance is phenominal.  Maybe we will start winning some
>>>    of those I/O benchmark tests now.
>>>
>>>                                        -Matt
>>>                                        Matthew Dillon
>>>                                        <dillon at backplane.com>
>>>
>>
>
>



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