Messages in this thread | | | Date | Wed, 23 Jan 2013 15:37:52 +0100 | From | Soeren Moch <> | Subject | Re: [PATCH v2] mm: dmapool: use provided gfp flags for all dma_alloc_coherent() calls |
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On 22.01.2013 19:13, Arnd Bergmann wrote: > On Monday 21 January 2013, Greg KH wrote: >>> >>> I don't know a lot about USB, but I always assumed that this was not >>> a normal condition and that there are only a couple of URBs per endpoint >>> used at a time. Maybe Greg or someone else with a USB background can >>> shed some light on this. >> >> There's no restriction on how many URBs a driver can have outstanding at >> once, and if you have a system with a lot of USB devices running at the >> same time, there could be lots of URBs in flight depending on the number >> of host controllers and devices and drivers being used.
I only use one host controller and (in this test) two usb devices with the same driver.
> Ok, thanks for clarifying that. I read some more of the em28xx driver, > and while it does have a bunch of URBs in flight, there are only five > audio and five video URBs that I see simultaneously being submitted, > and then resubmitted from their completion handlers. I think this > means that there should be 10 URBs active at any given time in this > driver, which does not explain why we get 256 allocations.
I think the audio part of the em28xx bridge is not used in my DVB tests.
Are there other allocations from orion-ehci directly? Maybe something special for isochronous transfers (since there is no problem with my other dvb sticks using bulk transfers)?
> I also noticed that the initial submissions are all atomic but don't > need to, so it may be worth trying the patch below, which should also > help in low-memory situations. We could also try moving the resubmission > into a workqueue in order to let those be GFP_KERNEL, but I don't think > that will help.
I built a linux-3.7.4 with the em28xx patch and both of your dma-mapping.c patches. I still see the ERROR: 1024 KiB atomic DMA coherent pool is too small!
Soeren
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