linux-kernel - Re: [PATCH] Increase usbfs bulk buffer size

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Date:	Fri, 19 Aug 2011 12:45:42 +0200
From:	Markus Rechberger <mrechberger@...il.com>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	Greg Kroah-Hartman <gregkh@...e.de>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Increase usbfs bulk buffer size

On Fri, Aug 19, 2011 at 8:23 AM, Oliver Neukum <oliver@...kum.org> wrote:
> Am Mittwoch, 17. August 2011, 19:44:16 schrieb Markus Rechberger:
>> I understand that USBFS is not 100% optimized, although we are already
>> using 3-4 times that much buffer with isochronous and it was working
>> fine for years so far as long as the system doesn't run out of memory
>> .. but even kerneldrivers would have issues with it in such a
>> situation.
>
> The problem is not what happens on your test system dedicated to this use.
> There it'll work. But you allowed everybody else to make the kernel request
> the second largest chunk of memory there is. On a otherwise busy system
> with fragmented memory this is not good.
>
> As I said, you want scatter/gather if you need this.
> There still would be the problem with the API, but if this is really a problem,
> you could define a new ioctl()
>

let's say there are a few thousand users of the 190k isochronous implementation.
I don't want to add more complex code to the kernel, if it's not
accepted I'm okay with it,
since I know the performance impact I can recommend it to those who
are interested in it.
Our software works without it anyway, and Bulk is just for special use
in our case.

Best Regards,
Markus
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