From: Dietmar Eggemann <dietmar.eggemann@arm.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, juri.lelli@arm.com
Subject: Re: [PATCH 1/4] sched/fair: Optimize sum computation with a lookup table
Date: Mon, 11 Apr 2016 17:59:11 +0100 [thread overview]
Message-ID: <570BD7DF.6070400@arm.com> (raw)
In-Reply-To: <1460327765-18024-2-git-send-email-yuyang.du@intel.com>
On 10/04/16 23:36, Yuyang Du wrote:
> __compute_runnable_contrib() uses a loop to compute sum, whereas a
> table loopup can do it faster in a constant time.
>
> The following python script can be used to generate the constants:
>
> print " #: yN_inv yN_sum"
> print "-----------------------"
> y = (0.5)**(1/32.0)
> x = 2**32
> xx = 1024
> for i in range(0, 32):
> if i == 0:
> x = x-1
> xx = xx*y
> else:
> x = x*y
> xx = int(xx*y + 1024*y)
> print "%2d: %#x %8d" % (i, int(x), int(xx))
>
> print " #: sum_N32"
> print "------------"
> xxx = xx
> for i in range(0, 11):
> if i == 0:
> xxx = xx
> else:
> xxx = xxx/2 + xx
> print "%2d: %8d" % (i, xxx)
>
IMHO, it would be nice to add this to the existing tool from the patch
header of commit 5b51f2f80b3b
("sched: Make __update_entity_runnable_avg() fast") simply because people
already use this one to tweak their pelt tables. Maybe something like
diff --git a/pelt.c b/pelt.c
index 63e32d1d18b0..b36194e8bb9c 100644
--- a/pelt.c
+++ b/pelt.c
@@ -6,6 +6,8 @@
const long WMULT_CONST = ((1UL << N) - 1);
double y;
+int ld_avg_max_n;
+double sum_fl_n;
long runnable_avg_yN_inv[N];
void calc_mult_inv() {
@@ -42,6 +44,7 @@ void calc_yn_sum(int n)
printf("%2d: %8.0f %8.0f %8.0f\n", i, sum, sum_fl,
sum_fl - sum);
}
+ sum_fl_n = sum_fl;
printf("\n");
}
@@ -55,14 +58,29 @@ void calc_conv(long n) {
n = mult_inv(n, 1) + 1024;
i++;
} while (n != old_n);
+ ld_avg_max_n = i - 1;
printf("%d> %ld\n", i - 1, n);
printf("\n");
}
+void calc_acc_sum() {
+ int i = 1;
+ double sum = sum_fl_n;
+ int periods = ld_avg_max_n/N + 1;
+
+ printf("sum acc\n");
+
+ do {
+ printf("%2d: %8.0f\n", i, sum);
+ sum = floor(sum/2 + sum_fl_n);
+ } while (++i <= periods);
+}
+
void main() {
y = pow(0.5, 1/(double)N);
calc_mult_inv();
calc_conv(1024);
calc_yn_sum(N);
+ calc_acc_sum();
}
[...]
next prev parent reply other threads:[~2016-04-11 16:59 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-10 22:36 [PATCH 0/4] Optimize sched avg computation and implement flat util hierarchy Yuyang Du
2016-04-10 22:36 ` [PATCH 1/4] sched/fair: Optimize sum computation with a lookup table Yuyang Du
2016-04-11 9:08 ` Vincent Guittot
2016-04-11 10:41 ` Juri Lelli
2016-04-11 19:12 ` Yuyang Du
2016-04-12 10:14 ` Juri Lelli
2016-04-12 18:07 ` Yuyang Du
2016-04-13 9:11 ` Juri Lelli
2016-04-11 16:59 ` Dietmar Eggemann [this message]
2016-04-11 19:17 ` Yuyang Du
2016-04-12 14:19 ` Peter Zijlstra
2016-04-12 18:12 ` Yuyang Du
2016-04-11 23:21 ` Joe Perches
2016-04-12 12:02 ` Juri Lelli
2016-04-11 23:07 ` Joe Perches
2016-04-10 22:36 ` [PATCH 2/4] sched/fair: Drop out incomplete current period when sched averages accrue Yuyang Du
2016-04-11 9:08 ` Vincent Guittot
2016-04-11 19:41 ` Yuyang Du
2016-04-12 11:56 ` Vincent Guittot
2016-04-12 21:09 ` Yuyang Du
2016-04-13 11:11 ` Vincent Guittot
2016-04-12 12:02 ` Dietmar Eggemann
2016-04-12 20:14 ` Yuyang Du
2016-04-13 4:04 ` Joe Perches
2016-04-13 8:40 ` Morten Rasmussen
2016-04-13 15:13 ` Dietmar Eggemann
2016-04-13 15:28 ` Vincent Guittot
2016-04-13 16:20 ` Vincent Guittot
2016-04-13 18:44 ` Yuyang Du
2016-04-14 12:52 ` Dietmar Eggemann
2016-04-14 20:05 ` Yuyang Du
2016-04-18 17:59 ` Yuyang Du
2016-04-10 22:36 ` [PATCH 3/4] sched/fair: Modify accumulated sums for load/util averages Yuyang Du
2016-04-11 17:14 ` Dietmar Eggemann
2016-04-10 22:36 ` [PATCH 4/4] sched/fair: Implement flat hierarchical structure for util_avg Yuyang Du
2016-04-11 12:29 ` Vincent Guittot
2016-04-11 20:37 ` Yuyang Du
2016-04-13 11:27 ` Vincent Guittot
2016-04-13 18:20 ` Yuyang Du
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