Message-ID: <1460111501.1800.28.camel@perches.com>
Subject: Re: [PATCH] sched/fair: Optimize sum computation with a lookup table
From: Joe Perches <joe@perches.com>
To: Yuyang Du <yuyang.du@intel.com>, peterz@infradead.org, mingo@kernel.org,
        linux-kernel@vger.kernel.org
Cc: bsegall@google.com, pjt@google.com, morten.rasmussen@arm.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com
Date: Fri, 08 Apr 2016 03:31:41 -0700
In-Reply-To: <1460081240-8074-1-git-send-email-yuyang.du@intel.com>
References: <1460081240-8074-1-git-send-email-yuyang.du@intel.com>
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On Fri, 2016-04-08 at 10:07 +0800, Yuyang Du wrote:
> __compute_runnable_contrib() uses a loop to compute sum, whereas a
> table lookup can do it faster in a constant time.

Perhaps this becomes rather fragile code overly dependent on the
current #define values of LOAD_AVG_MAX_N and LOAD_AVG_PERIOD.

Perhaps this comment just above the definitions of LOAD_AVG_MAX_N
and LOAD_AVG_PERIOD should be updated to include this new table:

?* Note: The tables runnable_avg_yN_inv and runnable_avg_yN_sum are
?* dependent on this value.

Perhaps the __ prefix for __accumulated_sum_N32 is odd as both of
the runnable_avg_yN_ tables are not __ prefixed.