From: Peter Zijlstra Date: Mon, 7 Sep 2015 13:09:15 +0000 (+0200) Subject: sched/fair: Optimize __update_load_avg() X-Git-Tag: firefly_0821_release~176^2~830^2~38 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=6115c793ca1a6e39c7c15159cbb47baa04009cb8;p=firefly-linux-kernel-4.4.55.git sched/fair: Optimize __update_load_avg() Prior to this patch; the line: scaled_delta_w = (delta_w * 1024) >> 10; which is the result of the default arch_scale_freq_capacity() function, turns into: 1b03: 49 89 d1 mov %rdx,%r9 1b06: 49 c1 e1 0a shl $0xa,%r9 1b0a: 49 c1 e9 0a shr $0xa,%r9 Which is silly; when made unsigned int, GCC recognises this as pointless ops and fails to emit them (confirmed on 4.9.3 and 5.1.1). Furthermore, afaict unsigned is actually the correct type for these fields anyway, as we've explicitly ruled out negative delta's earlier in this function. Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 7109047731eb..c3c5585292a6 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2551,7 +2551,7 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa, { u64 delta, scaled_delta, periods; u32 contrib; - int delta_w, scaled_delta_w, decayed = 0; + unsigned int delta_w, scaled_delta_w, decayed = 0; unsigned long scale_freq = arch_scale_freq_capacity(NULL, cpu); unsigned long scale_cpu = arch_scale_cpu_capacity(NULL, cpu);