ahci sata data overruns

[Wolfgang S. Rupprecht]

lee <lee at yun.yagibdah.de> writes:
> "Wolfgang S. Rupprecht" <wolfgang.rupprecht at gmail.com> writes:
>> The SSD in question is capable of 550 MByte/sec (Intel 520 SSD), while
>> the PCIE controller is only an x1 single lane controller which probbly
>> saturates the single lane at 480 MByte/sec.  I'm assuming (perhaps
>> incorrectly) that the controller is choking when it receives more data
>> from the SATA than it can transmit on the PCIE.
>>
>> The bootup kprintf's show a 6Mbit/sec negotiation, but later when I try
>> a transfer I see 130 MByte/sec transfers for a raw partition dd, hinting
>> strongly that it is now talking at 1.5Mbit/sec on the SATA.  I'm
>> wondering if it is silently downshifting the SATA speed.  In comparison,
>> a slower SSD rated at 250MBytes/sec (which can stay within the PCIE x1
>> lane budget) runs at full speed, of slightly over 250MBytes/sec on the
>> same controller.
>
> Have you tried to change the SATA cable?  You could switch them over and
> see what happens ...

Yes.  I've even swapped cables and SATA port between the good SSD that
runs at 250MBytes/sec and this one.  Same results and the other SSD
still ran at its 250MBytes/sec on the cable and port the mis-behaving
SSD was on.

-wolfgang
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