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The RCU Tasks Trace grace periods are too slow, as in 40x slower than those of RCU Tasks. This is due to my having assumed a one-second grace period was OK, and thus not having optimized any further. This commit provides the first step in this optimization process, namely by allowing the task_list scan backoff interval to be specified on a per-flavor basis, and then speeding up the scans for RCU Tasks Trace. However, kernels built with CONFIG_TASKS_TRACE_RCU_READ_MB=y continue to use the old slower backoff, consistent with that Kconfig option's goal of reducing IPIs. Link: https://lore.kernel.org/bpf/CAADnVQK_AiX+S_L_A4CQWT11XyveppBbQSQgH_qWGyzu_E8Yeg@mail.gmail.com/ Reported-by: Alexei Starovoitov <alexei.starovoitov@gmail.com> Cc: Daniel Borkmann <daniel@iogearbox.net> Cc: Jiri Olsa <jolsa@redhat.com> Cc: <bpf@vger.kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>