• Peter Zijlstra's avatar
    perf/core: Fix dynamic interrupt throttle · 55113176
    Peter Zijlstra authored
    There were two problems with the dynamic interrupt throttle mechanism,
    both triggered by the same action.
    
    When you (or perf_fuzzer) write a huge value into
    /proc/sys/kernel/perf_event_max_sample_rate the computed
    perf_sample_allowed_ns becomes 0. This effectively disables the whole
    dynamic throttle.
    
    This is fixed by ensuring update_perf_cpu_limits() never sets the
    value to 0. However, we allow disabling of the dynamic throttle by
    writing 100 to /proc/sys/kernel/perf_cpu_time_max_percent. This will
    generate a warning in dmesg.
    
    The second problem is that by setting the max_sample_rate to a huge
    number, the adaptive process can take a few tries, since it halfs the
    limit each time. Change that to directly compute a new value based on
    the observed duration.
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Cc: Andy Lutomirski <luto@amacapital.net>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: David Ahern <dsahern@gmail.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Stephane Eranian <eranian@google.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Vince Weaver <vincent.weaver@maine.edu>
    Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
    Signed-off-by: default avatarTan Xiaojun <tanxiaojun@huawei.com>
    Signed-off-by: default avatarSasha Levin <alexander.levin@verizon.com>
    55113176
core.c 212 KB