From mboxrd@z Thu Jan 1 00:00:00 1970 From: greg@kroah.com (Greg KH) Date: Thu, 15 Aug 2013 11:44:26 -0700 Subject: [Ksummit-2013-discuss] [ARM ATTEND] Trustzone-based security solution for ARM Linux In-Reply-To: <20130815183319.GE23006@n2100.arm.linux.org.uk> References: <20130815042812.GA8968@kroah.com> <20130815080532.GB7080@kroah.com> <20130815155652.GB14792@kroah.com> <20130815182600.GA22567@kroah.com> <20130815183319.GE23006@n2100.arm.linux.org.uk> Message-ID: <20130815184426.GA23581@kroah.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Aug 15, 2013 at 07:33:19PM +0100, Russell King - ARM Linux wrote: > On Thu, Aug 15, 2013 at 11:26:00AM -0700, Greg KH wrote: > > That's their decision, which is fine. Getting the Linux CAN stack > > "certified" might be a good goal for a manufacturer who wants to ship > > Linux for this type of system, although we all know how much those > > things really matter when it comes to technical issues :) > > If response times matter, and you're relying on software to produce > those response times, then you really need to look at threaded IRQs. > The standard Linux interrupt model sucks, especially if you have USB > enabled. Using USB withing a "trusted OS" situation isn't very wise for a number of reasons :) There is work happening on making USB host controllers use threaded interrups, the first round of changes just went into the usb-next branch in linux-next, and will show up in 3.12. It reduces the overhead of USB on ARM systems by a measurable ammount. There are more patches coming for this as well to fix up other related issues, and USB host controllers. > I'm still seeing upwards of 2.6ms servicing times for USB keyboards > and nice, which given that they are just a set of keys and a position > sensor is totally crazy. USB is not exactly a low-latency protocol. A lot happens for just those "key press" packets to make it to the machine. thanks, greg k-h