On Tue, 2018-06-19 at 17:45 -0700, Tadeusz Struk wrote: > On 06/19/2018 06:10 AM, Jarkko Sakkinen wrote: > > On Tue, Jun 12, 2018 at 10:58:26AM -0700, Tadeusz Struk wrote: > > > The TCG SAPI specification [1] defines a set of functions, which > > > allows applications to use the TPM device in either blocking or > > > non-blocking fashion. Each command defined by the specification > > > has a corresponding Tss2_Sys_<COMMAND>_Prepare() and > > > Tss2_Sys_<COMMAND>_Complete() call, which together with > > > Tss2_Sys_ExecuteAsync() is designed to allow asynchronous > > > mode of operation. Currently the TPM driver supports only > > > blocking calls, which doesn't allow asynchronous IO operations. > > > This patch changes it and adds support for nonblocking write and > > > a new poll function to enable applications, which want to take > > > advantage of this feature. The new functionality can be tested > > > using standard TPM tools implemented in [2], together with > > > modified TCTI from [3]. > > > > > > [1] https://trustedcomputinggroup.org/wp-content/uploads/TSS_SAPI > > > _Version-1.1_Revision-22_review_030918.pdf > > > [2] https://github.com/tpm2-software/tpm2-tools > > > [3] https://github.com/tstruk/tpm2-tss/tree/async > > > > For me the value is still a bit questionable. The benchmark looks a > > bit flakky to give much figures how this would work with real world > > workloads. > > > > I read James response and I also have to question why not just a > > worker thread in user space? TPM does only one command at a time > > anyways. > > > > Cannot take this in before I know that user space will (1) adapt to > > this and (2) gain value compared to a worker thread. > > > > Hi Jarkko, > Thanks for reviewing the patch. > There are applications/frameworks where a worker thread is not an > option. > Take for example the IoT use-cases and frameworks like IoT.js, or > "Node.js for IoT". > They are all single threaded, event-driven frameworks, using non- > blocking I/O as the base of their processing model. I'm slightly surprised by this statement. I thought IoT Node.js runtimes (of which there are far too many, so I haven't looked at all of them) use libuv or one of the forks: http://libuv.org/ As the basis for their I/O handling? While libuv can do polling for event driven interfaces it also support the worker thread model just as easily: http://docs.libuv.org/en/v1.x/threadpool.html > Similarly embedded applications, which are basically just a single > threaded event loop, quite often don't use threads because of > resources constrains. It's hard for me, as a kernel developer, to imagine any embedded scenario using the Linux kernel that would not allow threads unless the writers simply didn't bother with synchronization: The kernel schedules at the threads level and can't be configured not to use them plus threads are inherently more lightweight than processes so they're a natural fit for resource constrained scenarios. That's still not to say we shouldn't do this, but I've got to say I think the only consumers would be old fashioned C code: the code we used to write before we had thread libraries that did use signals and poll() for a single threaded event driven monolith (think green threads), because all the new webby languages use threading either explicitly or at the core of their operation. James
