On Tue, Apr 13, 2010 at 1:48 AM, Alan Stern <stern@rowland.harvard.edu> wrote:

quoted text
>> I never saw the mass storage driver enqueue more sg entries than
>> TRBS_PER_SEGMENT.  It's just Ramya's driver that has this behavior.  At
>> this point, we can't tell what he's doing without his source code.
>
> This directly contradicts Ramya's statement above: "When I am testing
> the default usb storage driver with 960 max_sectors Sarah saw ~120
> scatter-gather list entries."
>
> Evidently the two of you need to figure out exactly what happened.
> More tests can't hurt...

Sorry to confuse you but please find the scenario that resulted in the
above discussion. Initially, I was working on a UASP driver and was
seeing a timeout issue. So, during my debug process, I also tested the
default mass storage driver by increasing the max sectors to 960,
since our device is capable of supporting it. Here, I encountered a
similar issue and sent my logs to Sarah, requesting her help. At that
point, the logs had indicated that scatter gather list had 73 entries
(>63).

Later, I used the Sarah Sharp “xhci-large-tx” branch where
TRBS_PER_SEGMENT is set to 128, which was thought about as a temporary
fix. That is the reason I saw 120 scatter-gather list entries.
However, today I tested the default usb storage driver for more than
10 times by setting the TRBS_PER_SEGEMENT to 64 and I am unable to see
sg_list entries greater than 63. When I changed TRBS_PER_SEGMENT to
128 then I am seeing 120 sg_list entries. But, that still leaves my
issue in the unresolved state, since I am unable to do large transfers
consistently (with default mass storage driver) when max_sectors is
set to 960. I tried the same with EHCI driver (using USB2.0 port) and
it works fine without any issue. I aslo tried with USB 2.0 cable by
connecting it to USB 3.0 port and it works fine without any issues.
So, I guess it should either be a hardware issue or maybe something
related to xHCI driver. I can send the latest logs, if needed.

Thansk and Regards,
Ramya.
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