linux-kernel - Re: USB transfer_buffer allocations on 64bit systems

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Message-ID: <20100412115300.GM18855@one.firstfloor.org>
Date:	Mon, 12 Apr 2010 13:53:00 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Daniel Mack <daniel@...aq.de>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Alan Stern <stern@...land.harvard.edu>,
	linux-kernel@...r.kernel.org, Pedro Ribeiro <pedrib@...il.com>,
	akpm@...ux-foundation.org, Greg KH <gregkh@...e.de>,
	alsa-devel@...a-project.org, linux-usb@...r.kernel.org
Subject: Re: USB transfer_buffer allocations on 64bit systems

> Which is exactly what usb_buffer_alloc() does already. So at least for
> x86 you say this is the right thing to do? However, we don't necessarily
> need coherent memory on other platforms, which is why I hessitate to
> enforce that type of memory for all transfer_buffer allocations.

Yes today it's faster at least.

Probably we should have better interfaces for this, but we don't.

> 
> > Or just use GFP_KERNEL and pci_map_* later.
> 
> The USB core does this already, but at least on Pedro's machine, this
> seems unsufficient. Unfortunately, I can't reproduce the issue yet, even
> with more than 4GB of RAM installed.

Then something must be broken in Pedro's system and likely other drivers
will also not work. I don't think it should be worked around in the USB layer.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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