Alexander Lobakin wrote: > From: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> > Date: Tue, 20 Feb 2024 22:03:39 +0100 > > > The BPF_TEST_RUN code in XDP live frame mode creates a new page pool > > each time it is called and uses that to allocate the frames used for the > > XDP run. This works well if the syscall is used with a high repetitions > > number, as it allows for efficient page recycling. However, if used with > > a small number of repetitions, the overhead of creating and tearing down > > the page pool is significant, and can even lead to system stalls if the > > syscall is called in a tight loop. > > > > Now that we have a persistent system page pool instance, it becomes > > pretty straight forward to change the test_run code to use it. The only > > wrinkle is that we can no longer rely on a custom page init callback > > from page_pool itself; instead, we change the test_run code to write a > > random cookie value to the beginning of the page as an indicator that > > the page has been initialised and can be re-used without copying the > > initial data again. > > > > The cookie is a random 128-bit value, which means the probability that > > we will get accidental collisions (which would lead to recycling the > > wrong page values and reading garbage) is on the order of 2^-128. This > > is in the "won't happen before the heat death of the universe" range, so > > this marking is safe for the intended usage. > > > > Reviewed-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx> > > Tested-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx> > > Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> > > Hey, > > What's the status of this series, now that the window is open? > > Thanks, > Olek Hi Toke, I read the thread from top to bottom so seems someone else notices the 2^128 is unique numbers not the collision probability. Anywaays I'm still a bit confused, whats the use case here? Maybe I need to understand what this XDP live frame mode is better? Could another solution be to avoid calling BPF_TEST_RUN multiple times in a row? Or perhaps have a BPF_SETUP_RUN that does the config and lets BPF_TEST_RUN skip the page allocation? Another idea just have the first run of BPF_TEST_RUN init a page pool and not destroy it. Thanks, John
