linux-kernel - Re: [RESEND PATCH 2/3 v5] sched: Rewrite per entity runnable load average tracking

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Date:	Tue, 21 Oct 2014 16:32:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org, pjt@...gle.com,
	bsegall@...gle.com, arjan.van.de.ven@...el.com,
	len.brown@...el.com, rafael.j.wysocki@...el.com,
	alan.cox@...el.com, mark.gross@...el.com, fengguang.wu@...el.com
Subject: Re: [RESEND PATCH 2/3 v5] sched: Rewrite per entity runnable load
 average tracking

On Fri, Oct 10, 2014 at 10:21:56AM +0800, Yuyang Du wrote:
> +static __always_inline u64 decay_load(u64 val, u64 n)
> +{
> +	if (likely(val <= UINT_MAX))
> +		return decay_load32(val, n);
> +
> +	return mul_u64_u32_shr(val, decay_load32(1 << 15, n), 15);
> +}

This still doesn't make any sense, why not put that mul_u64_u32_shr()
into decay_load() and be done with it?

---
 kernel/sched/fair.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b78280c59b46..67c08d4a3df8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2231,9 +2231,8 @@ static __always_inline u64 decay_load(u64 val, u64 n)
 		local_n %= LOAD_AVG_PERIOD;
 	}
 
-	val *= runnable_avg_yN_inv[local_n];
-	/* We don't use SRR here since we always want to round down. */
-	return val >> 32;
+	val = mul_u64_u32_shr(val, runnable_avg_yN_inv[local_n], 32);
+	return val;
 }
 
 /*
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