On Wed, Jan 09, 2019 at 08:17:15AM -0500, Ian Goldberg wrote: > On Wed, Jan 09, 2019 at 08:42:18PM +1100, Todd Hubers wrote: > > There are early plans to distribute crypto operations across multiple cores > > [https://trac.torproject.org/projects/tor/ticket/1749], but there might be > > a better way. > > > > (I registered, but I couldn't find a way to annotate the ticket, so I'm > > emailing for now) > > > > The ticket states the reason being to saturate the bandwidth available (by > > using all the cores as efficiently as possible). > > > > I don't understand why a relay needs to have a "main thread". Network > > traffic arrives as an async operation and can be sent back out > > asynchronously. So a final strategy shouldn't have a central thread. The > > main thread might still be needed for startup, runtime adjustment, and > > system upkeep, but not for the core network-crypto processing; that should > > never need to touch the main thread. > > > > The current proposal speaks about multi-threading crypto operations, let's > > call that "A) Speed - Speeding up processing of a single cell". Instead, I > > propose "B) Concurrency - Restructuring so multiple cells can be processed > > concurrently". > > > > A cell of data should arrive via IO-Completion thread on a random CPU core, > > have crypto transformation applied on the same one core, then be dispatched > > onward out via the network. This seems to be quite a simple approach where > > I would think crypto code can remain the same "single-threaded" > > implementation. > > > > Approach [A] will have diminishing returns as the number of cores > > increases. You can only break up a cell unit of work so much until you're > > encrypting one byte per cpu core. However, with approach [B], if you have > > millions of CPU cores (as an extreme) you can be processing millions of > > cells concurrently. Therefore, I believe approach [B] would be more > > scalable. > > > > What do you think? > > You'll have troubles if cells *on the same circuit* try to be processed > in parallel on different cores, at least with the current circuit-level > crypto. But, once circuits are established, handing each circuit to a > different thread/core (or more clever worker structure) is something > that I think at least boradly makes sense, and indeed I have been > proposing to have my students work on.
(Of course, this only is even relevant for the very highest-bandwidth nodes; my own node, for example, running on 5-year-old hardware with no special configuration, was pushing 400 Mbps last month, with one core at 80%, one at 11%, one at 6%, and the rest trivially small.) -- Ian Goldberg Professor and University Research Chair Cheriton School of Computer Science University of Waterloo _______________________________________________ tor-dev mailing list tor-dev@lists.torproject.org https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev
