"Wolfgang S. Rupprecht" <wolfgang.rupprecht@xxxxxxxxx> writes: > Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> writes: >> On Thu, 08 Nov 2012 09:43:29 -0800 >> "Wolfgang S. Rupprecht" <wolfgang.rupprecht@xxxxxxxxx> wrote: >>> Can someone familiar with how the AHCI driver works confirm that data >>> overruns on a SATA link can cause the driver to down-shift the SATA >>> speed 6->3->1.5 Gbits/sec. I don't see any kprintf's but I notice that >>> a high speed SSD acting as if the SATA were running at 1.5 Gbits/sec. >> >> It has a set of heuristics based upon error rate over time. >> >> I'm not sure what you mean by "data overruns" however > > 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 ... -- Fedora 17 -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines Have a question? Ask away: http://ask.fedoraproject.org
