sched: framework for sched_mc/smt_power_savings=N

Impact: extend range of /sys/devices/system/cpu/sched_mc_power_savings

Currently the sched_mc/smt_power_savings variable is a boolean,
which either enables or disables topology based power savings.
This patch extends the behaviour of the variable from boolean to
multivalued, such that based on the value, we decide how
aggressively do we want to perform powersavings balance at
appropriate sched domain based on topology.

Variable levels of power saving tunable would benefit end user to
match the required level of power savings vs performance
trade-off depending on the system configuration and workloads.

This version makes the sched_mc_power_savings global variable to
take more values (0,1,2).  Later versions can have a single
tunable called sched_power_savings instead of
sched_{mc,smt}_power_savings.

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 14 insertions, 3 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index b309027bf9e8..56b285cd5350 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7906,14 +7906,25 @@ int arch_reinit_sched_domains(void)
 static ssize_t sched_power_savings_store(const char *buf, size_t count, int smt)
 {
         int ret;
+        unsigned int level = 0;
 
-        if (buf[0] != '0' && buf[0] != '1')
+        if (sscanf(buf, "%u", &level) != 1)
+                return -EINVAL;
+
+        /*
+         * level is always be positive so don't check for
+         * level < POWERSAVINGS_BALANCE_NONE which is 0
+         * What happens on 0 or 1 byte write,
+         * need to check for count as well?
+         */
+
+        if (level >= MAX_POWERSAVINGS_BALANCE_LEVELS)
                 return -EINVAL;
 
         if (smt)
-                sched_smt_power_savings = (buf[0] == '1');
+                sched_smt_power_savings = level;
         else
-                sched_mc_power_savings = (buf[0] == '1');
+                sched_mc_power_savings = level;
 
         ret = arch_reinit_sched_domains();