linux-kernel - Kernel driver vs libusb performance

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Message-ID: <CAFub=KQK9Qm1vDAetJc53O+mTZCgnaGDw9hYgeSZ76KCX_XSyQ@mail.gmail.com>
Date:	Fri, 11 Jan 2013 11:53:36 +0200
From:	Ozan Çağlayan <ozancag@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <greg@...ah.com>
Subject: Kernel driver vs libusb performance

Hi,

I have a device which I'm currently accessing using libusb. It's
basically a HID compliant USB device. It reports 32bytes of data with
a time resolution of 128Hz, e.g. I have to read and store 32bytes each
1/128 second. One performance drawback is that those 32bytes chunks
are encrypted with AES so once I receive them through the USB endpoint
I first decrypt them.

So 128Hz is quite a low polling frequency and can be handled in a
single-thread using a modern CPU, but I'm planning to run this loop on
a Raspberry Pi or namely low-end, cheap embedded processors. I'm also
using Python which is significantly slow on Raspberry Pi.

So I wonder whether writing a kernel driver which decrypts the packets
using in-kernel crypto API and then exposing them through a character
device node would bring a performance gain at all. At least on the
userspace side I may get rid of all the bus searching, crypto key
generation, fetching and decrypting boilerplate, am I in the wrong
way?

Thanks,

-- 
Ozan Çağlayan
Research Assistant
Galatasaray University - Computer Engineering Dept.
http://www.ozancaglayan.com
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