Ian Abbott wrote:
On 28/09/2005 18:24, Paulo Marques wrote:
If my math is correct, these 2 entries are taking 46Mb + 30Mb -> 76Mb on
a computer that has only 112Mb available for the entire system. So
something is eating memory away like crazy.
Is there a known problem with this driver? Are there some patches that
I can try out?
It's a known problem. No patches yet, I'm afraid. What happens is that
the driver dynamically allocates URBs and transfer buffers for
everything written to it and submits them to the USB device's bulk
transfer queue where they sit until the UART has dealt with them.
Whenever the TTY layer asks the driver how much data it can write, the
answer from the driver is "lots", so there is no throttling of the
'write' path back to the application. The driver really needs to
modulate this answer according to how much data is queued up (and
possibly how quickly the queued data can be transmitted).
Sorry for replying so late, but I've been reading LDD3 and looking at
the ftdi sources...
Anyway, are you sure this is the problem I was reporting?
I might be reading this the wrong way, but it seems that you're talking
about a userspace application writing too much data too fast to the
serial port, while my problem is exactly the opposite: the application
just writes a few bytes to request a frame (a CCD frame, nothing to do
with USB frames ;) ) but then the device tries to send 800Kb to the
application that is read'ing as fast as it can.
Could this be caused by the same RCU problems I've been reading on LKML,
i.e., does this trigger a code path inside the USB core (or USB
controller) that uses RCU that might be hitting the same problem?
I'll do some more tests with a more recent kernel, to try to get more
debug information...
--
Paulo Marques - www.grupopie.com
The rule is perfect: in all matters of opinion our
adversaries are insane.
Mark Twain
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