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charset="UTF-8" BinderStats::inc_bc() and BinderStats::inc_br() increment command and return statistics counters on every Binder transaction and reply using Atomic::fetch_add(1, Relaxed), discarding the returned previous value. Because the return value of fetch_add() is unused in Rust but must still be produced by the underlying value-returning atomic RMW helper (atomic_fetch_add_relaxed()), the compiler is forced to emit a value-returning atomic operation (LDADD on arm64 with LSE, or LOCK XADD on x86) instead of a non-value-returning atomic add (STADD on arm64, or LOCK ADD on x86). On arm64 CPUs with LSE, value-returning LDADD requires a round-trip response from the L2/interconnect to populate the destination register, whereas non-value-returning STADD (encoded as LDADD with WZR as the destination register) may be executed as a far atomic without waiting for the old value to return to the core. Switch BinderStats::inc_bc() and BinderStats::inc_br() from fetch_add(1, Relaxed) to add(1, Relaxed) so they lower to atomic_add() and emit non-value-returning atomic increments. This also matches the C Binder driver, which uses atomic_inc() for these statistics counters in binder_thread_write() and binder_stat_br(). Reviewed-by: Boqun Feng Reviewed-by: FUJITA Tomonori Signed-off-by: Jenhao Chen --- Changes in v2: - Drop "No functional change intended." from commit description (Boqun Feng). - Collect Reviewed-by tags from Boqun Feng and FUJITA Tomonori. - Link to v1: https://lore.kernel.org/r/20261031030801.4100693-1-jenhaochen@google.com/ drivers/android/binder/stats.rs | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/android/binder/stats.rs b/drivers/android/binder/stats.rs index ec81dc7747db..68cb0cf48865 100644 --- a/drivers/android/binder/stats.rs +++ b/drivers/android/binder/stats.rs @@ -32,14 +32,14 @@ impl BinderStats { pub(crate) fn inc_bc(&self, bc: u32) { let idx = _IOC_NR(bc) as usize; if let Some(bc_ref) = self.bc.get(idx) { - bc_ref.fetch_add(1, Relaxed); + bc_ref.add(1, Relaxed); } } pub(crate) fn inc_br(&self, br: u32) { let idx = _IOC_NR(br) as usize; if let Some(br_ref) = self.br.get(idx) { - br_ref.fetch_add(1, Relaxed); + br_ref.add(1, Relaxed); } } -- 2.56.0.317.g454f8302e1-goog