The frequency transition latency from pmin to pmax is observed to be in few
millisecond granurality. And it usually happens to take a performance penalty
during sudden frequency rampup requests.
This patch set solves this problem by using a chip-level entity called "global
pstates". Global pstate manages elements across other dependent core chiplets.
Typically, the element that needs to be managed is the voltage setting.
So by holding global pstates higher than local pstate for some amount of time
( ~5 seconds) the subsequent rampups could be made faster.
(1/2) patch removes the flag from cpufreq_policy->driver_data, so that it can
be used for tracking global pstates.
(2/2) patch adds code for global pstate management.
- The iozone results with this patchset, shows improvements in almost all cases.
- YCSB workload on redis with various target operations per second shows
better MaxLatency with this patch.
Changes from v1:
- Fixed coding style
- Added a routine to reset global_pstate_info instead of hacky memset
- Handled case where cpufreq_table_validate_and_show() fails
- changed int queue_gpstate_timer() to void queue_gpstate_timer()
Changes from v2:
- dropped the unreated change.
Akshay Adiga (1):
cpufreq: powernv: Ramp-down global pstate slower than local-pstate
Shilpasri G Bhat (1):
cpufreq: powernv: Remove flag use-case of policy->driver_data
drivers/cpufreq/powernv-cpufreq.c | 269 ++++++++++++++++++++++++++++++++++++--
1 file changed, 256 insertions(+), 13 deletions(-)
--
2.5.5
From: Shilpasri G Bhat <[email protected]>
commit 1b0289848d5d ("cpufreq: powernv: Add sysfs attributes to show
throttle stats") used policy->driver_data as a flag for one-time creation
of throttle sysfs files. Instead of this use 'kernfs_find_and_get()' to
check if the attribute already exists. This is required as
policy->driver_data is used for other purposes in the later patch.
Signed-off-by: Shilpasri G Bhat <[email protected]>
Signed-off-by: Akshay Adiga <[email protected]>
Acked-by: Viresh Kumar <[email protected]>
---
drivers/cpufreq/powernv-cpufreq.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
index 39ac78c..e2e2219 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -455,13 +455,15 @@ static int powernv_cpufreq_target_index(struct cpufreq_policy *policy,
static int powernv_cpufreq_cpu_init(struct cpufreq_policy *policy)
{
int base, i;
+ struct kernfs_node *kn;
base = cpu_first_thread_sibling(policy->cpu);
for (i = 0; i < threads_per_core; i++)
cpumask_set_cpu(base + i, policy->cpus);
- if (!policy->driver_data) {
+ kn = kernfs_find_and_get(policy->kobj.sd, throttle_attr_grp.name);
+ if (!kn) {
int ret;
ret = sysfs_create_group(&policy->kobj, &throttle_attr_grp);
@@ -470,11 +472,8 @@ static int powernv_cpufreq_cpu_init(struct cpufreq_policy *policy)
policy->cpu);
return ret;
}
- /*
- * policy->driver_data is used as a flag for one-time
- * creation of throttle sysfs files.
- */
- policy->driver_data = policy;
+ } else {
+ kernfs_put(kn);
}
return cpufreq_table_validate_and_show(policy, powernv_freqs);
}
--
2.5.5
The frequency transition latency from pmin to pmax is observed to be in
few millisecond granurality. And it usually happens to take a performance
penalty during sudden frequency rampup requests.
This patch set solves this problem by using an entity called "global
pstates". The global pstate is a Chip-level entity, so the global entitiy
(Voltage) is managed across the cores. The local pstate is a Core-level
entity, so the local entity (frequency) is managed across threads.
This patch brings down global pstate at a slower rate than the local
pstate. Hence by holding global pstates higher than local pstate makes
the subsequent rampups faster.
A per policy structure is maintained to keep track of the global and
local pstate changes. The global pstate is brought down using a parabolic
equation. The ramp down time to pmin is set to ~5 seconds. To make sure
that the global pstates are dropped at regular interval , a timer is
queued for every 2 seconds during ramp-down phase, which eventually brings
the pstate down to local pstate.
Iozone results show fairly consistent performance boost.
YCSB on redis shows improved Max latencies in most cases.
Iozone write/rewite test were made with filesizes 200704Kb and 401408Kb
with different record sizes . The following table shows IOoperations/sec
with and without patch.
Iozone Results ( in op/sec) ( mean over 3 iterations )
---------------------------------------------------------------------
file size- with without %
recordsize-IOtype patch patch change
----------------------------------------------------------------------
200704-1-SeqWrite 1616532 1615425 0.06
200704-1-Rewrite 2423195 2303130 5.21
200704-2-SeqWrite 1628577 1602620 1.61
200704-2-Rewrite 2428264 2312154 5.02
200704-4-SeqWrite 1617605 1617182 0.02
200704-4-Rewrite 2430524 2351238 3.37
200704-8-SeqWrite 1629478 1600436 1.81
200704-8-Rewrite 2415308 2298136 5.09
200704-16-SeqWrite 1619632 1618250 0.08
200704-16-Rewrite 2396650 2352591 1.87
200704-32-SeqWrite 1632544 1598083 2.15
200704-32-Rewrite 2425119 2329743 4.09
200704-64-SeqWrite 1617812 1617235 0.03
200704-64-Rewrite 2402021 2321080 3.48
200704-128-SeqWrite 1631998 1600256 1.98
200704-128-Rewrite 2422389 2304954 5.09
200704-256 SeqWrite 1617065 1616962 0.00
200704-256-Rewrite 2432539 2301980 5.67
200704-512-SeqWrite 1632599 1598656 2.12
200704-512-Rewrite 2429270 2323676 4.54
200704-1024-SeqWrite 1618758 1616156 0.16
200704-1024-Rewrite 2431631 2315889 4.99
401408-1-SeqWrite 1631479 1608132 1.45
401408-1-Rewrite 2501550 2459409 1.71
401408-2-SeqWrite 1617095 1626069 -0.55
401408-2-Rewrite 2507557 2443621 2.61
401408-4-SeqWrite 1629601 1611869 1.10
401408-4-Rewrite 2505909 2462098 1.77
401408-8-SeqWrite 1617110 1626968 -0.60
401408-8-Rewrite 2512244 2456827 2.25
401408-16-SeqWrite 1632609 1609603 1.42
401408-16-Rewrite 2500792 2451405 2.01
401408-32-SeqWrite 1619294 1628167 -0.54
401408-32-Rewrite 2510115 2451292 2.39
401408-64-SeqWrite 1632709 1603746 1.80
401408-64-Rewrite 2506692 2433186 3.02
401408-128-SeqWrite 1619284 1627461 -0.50
401408-128-Rewrite 2518698 2453361 2.66
401408-256-SeqWrite 1634022 1610681 1.44
401408-256-Rewrite 2509987 2446328 2.60
401408-512-SeqWrite 1617524 1628016 -0.64
401408-512-Rewrite 2504409 2442899 2.51
401408-1024-SeqWrite 1629812 1611566 1.13
401408-1024-Rewrite 2507620 2442968 2.64
Tested with YCSB workload (50% update + 50% read) over redis for 1 million
records and 1 million operation. Each test was carried out with target
operations per second and persistence disabled.
Max-latency (in us)( mean over 5 iterations )
---------------------------------------------------------------
op/s Operation with patch without patch %change
---------------------------------------------------------------
15000 Read 61480.6 50261.4 22.32
15000 cleanup 215.2 293.6 -26.70
15000 update 25666.2 25163.8 2.00
25000 Read 32626.2 89525.4 -63.56
25000 cleanup 292.2 263.0 11.10
25000 update 32293.4 90255.0 -64.22
35000 Read 34783.0 33119.0 5.02
35000 cleanup 321.2 395.8 -18.8
35000 update 36047.0 38747.8 -6.97
40000 Read 38562.2 42357.4 -8.96
40000 cleanup 371.8 384.6 -3.33
40000 update 27861.4 41547.8 -32.94
45000 Read 42271.0 88120.6 -52.03
45000 cleanup 263.6 383.0 -31.17
45000 update 29755.8 81359.0 -63.43
(test without target op/s)
47659 Read 83061.4 136440.6 -39.12
47659 cleanup 195.8 193.8 1.03
47659 update 73429.4 124971.8 -41.24
Signed-off-by: Akshay Adiga <[email protected]>
Reviewed-by: Gautham R. Shenoy <[email protected]>
Acked-by: Viresh Kumar <[email protected]>
---
drivers/cpufreq/powernv-cpufreq.c | 258 ++++++++++++++++++++++++++++++++++++--
1 file changed, 251 insertions(+), 7 deletions(-)
diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
index e2e2219..144c732 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -36,12 +36,56 @@
#include <asm/reg.h>
#include <asm/smp.h> /* Required for cpu_sibling_mask() in UP configs */
#include <asm/opal.h>
+#include <linux/timer.h>
#define POWERNV_MAX_PSTATES 256
#define PMSR_PSAFE_ENABLE (1UL << 30)
#define PMSR_SPR_EM_DISABLE (1UL << 31)
#define PMSR_MAX(x) ((x >> 32) & 0xFF)
+#define MAX_RAMP_DOWN_TIME 5120
+/*
+ * On an idle system we want the global pstate to ramp-down from max value to
+ * min over a span of ~5 secs. Also we want it to initially ramp-down slowly and
+ * then ramp-down rapidly later on.
+ *
+ * This gives a percentage rampdown for time elapsed in milliseconds.
+ * ramp_down_percentage = ((ms * ms) >> 18)
+ * ~= 3.8 * (sec * sec)
+ *
+ * At 0 ms ramp_down_percent = 0
+ * At 5120 ms ramp_down_percent = 100
+ */
+#define ramp_down_percent(time) ((time * time) >> 18)
+
+/* Interval after which the timer is queued to bring down global pstate */
+#define GPSTATE_TIMER_INTERVAL 2000
+
+/**
+ * struct global_pstate_info - Per policy data structure to maintain history of
+ * global pstates
+ * @highest_lpstate: The local pstate from which we are ramping down
+ * @elapsed_time: Time in ms spent in ramping down from
+ * highest_lpstate
+ * @last_sampled_time: Time from boot in ms when global pstates were
+ * last set
+ * @last_lpstate,last_gpstate: Last set values for local and global pstates
+ * @timer: Is used for ramping down if cpu goes idle for
+ * a long time with global pstate held high
+ * @gpstate_lock: A spinlock to maintain synchronization between
+ * routines called by the timer handler and
+ * governer's target_index calls
+ */
+struct global_pstate_info {
+ int highest_lpstate;
+ unsigned int elapsed_time;
+ unsigned int last_sampled_time;
+ int last_lpstate;
+ int last_gpstate;
+ spinlock_t gpstate_lock;
+ struct timer_list timer;
+};
+
static struct cpufreq_frequency_table powernv_freqs[POWERNV_MAX_PSTATES+1];
static bool rebooting, throttled, occ_reset;
@@ -94,6 +138,17 @@ static struct powernv_pstate_info {
int nr_pstates;
} powernv_pstate_info;
+static inline void reset_gpstates(struct cpufreq_policy *policy)
+{
+ struct global_pstate_info *gpstates = policy->driver_data;
+
+ gpstates->highest_lpstate = 0;
+ gpstates->elapsed_time = 0;
+ gpstates->last_sampled_time = 0;
+ gpstates->last_lpstate = 0;
+ gpstates->last_gpstate = 0;
+}
+
/*
* Initialize the freq table based on data obtained
* from the firmware passed via device-tree
@@ -285,6 +340,7 @@ static inline void set_pmspr(unsigned long sprn, unsigned long val)
struct powernv_smp_call_data {
unsigned int freq;
int pstate_id;
+ int gpstate_id;
};
/*
@@ -343,19 +399,21 @@ static unsigned int powernv_cpufreq_get(unsigned int cpu)
* (struct powernv_smp_call_data *) and the pstate_id which needs to be set
* on this CPU should be present in freq_data->pstate_id.
*/
-static void set_pstate(void *freq_data)
+static void set_pstate(void *data)
{
unsigned long val;
- unsigned long pstate_ul =
- ((struct powernv_smp_call_data *) freq_data)->pstate_id;
+ struct powernv_smp_call_data *freq_data = data;
+ unsigned long pstate_ul = freq_data->pstate_id;
+ unsigned long gpstate_ul = freq_data->gpstate_id;
val = get_pmspr(SPRN_PMCR);
val = val & 0x0000FFFFFFFFFFFFULL;
pstate_ul = pstate_ul & 0xFF;
+ gpstate_ul = gpstate_ul & 0xFF;
/* Set both global(bits 56..63) and local(bits 48..55) PStates */
- val = val | (pstate_ul << 56) | (pstate_ul << 48);
+ val = val | (gpstate_ul << 56) | (pstate_ul << 48);
pr_debug("Setting cpu %d pmcr to %016lX\n",
raw_smp_processor_id(), val);
@@ -424,6 +482,110 @@ next:
}
}
+/**
+ * calc_global_pstate - Calculate global pstate
+ * @elapsed_time: Elapsed time in milliseconds
+ * @local_pstate: New local pstate
+ * @highest_lpstate: pstate from which its ramping down
+ *
+ * Finds the appropriate global pstate based on the pstate from which its
+ * ramping down and the time elapsed in ramping down. It follows a quadratic
+ * equation which ensures that it reaches ramping down to pmin in 5sec.
+ */
+static inline int calc_global_pstate(unsigned int elapsed_time,
+ int highest_lpstate, int local_pstate)
+{
+ int pstate_diff;
+
+ /*
+ * Using ramp_down_percent we get the percentage of rampdown
+ * that we are expecting to be dropping. Difference between
+ * highest_lpstate and powernv_pstate_info.min will give a absolute
+ * number of how many pstates we will drop eventually by the end of
+ * 5 seconds, then just scale it get the number pstates to be dropped.
+ */
+ pstate_diff = ((int)ramp_down_percent(elapsed_time) *
+ (highest_lpstate - powernv_pstate_info.min)) / 100;
+
+ /* Ensure that global pstate is >= to local pstate */
+ if (highest_lpstate - pstate_diff < local_pstate)
+ return local_pstate;
+ else
+ return highest_lpstate - pstate_diff;
+}
+
+static inline void queue_gpstate_timer(struct global_pstate_info *gpstates)
+{
+ unsigned int timer_interval;
+
+ /*
+ * Setting up timer to fire after GPSTATE_TIMER_INTERVAL ms, But
+ * if it exceeds MAX_RAMP_DOWN_TIME ms for ramp down time.
+ * Set timer such that it fires exactly at MAX_RAMP_DOWN_TIME
+ * seconds of ramp down time.
+ */
+ if ((gpstates->elapsed_time + GPSTATE_TIMER_INTERVAL)
+ > MAX_RAMP_DOWN_TIME)
+ timer_interval = MAX_RAMP_DOWN_TIME - gpstates->elapsed_time;
+ else
+ timer_interval = GPSTATE_TIMER_INTERVAL;
+
+ mod_timer_pinned(&gpstates->timer, jiffies +
+ msecs_to_jiffies(timer_interval));
+}
+
+/**
+ * gpstate_timer_handler
+ *
+ * @data: pointer to cpufreq_policy on which timer was queued
+ *
+ * This handler brings down the global pstate closer to the local pstate
+ * according quadratic equation. Queues a new timer if it is still not equal
+ * to local pstate
+ */
+void gpstate_timer_handler(unsigned long data)
+{
+ struct cpufreq_policy *policy = (struct cpufreq_policy *)data;
+ struct global_pstate_info *gpstates = policy->driver_data;
+ int gpstate_id;
+ unsigned int time_diff = jiffies_to_msecs(jiffies)
+ - gpstates->last_sampled_time;
+ struct powernv_smp_call_data freq_data;
+
+ if (!spin_trylock(&gpstates->gpstate_lock))
+ return;
+
+ gpstates->last_sampled_time += time_diff;
+ gpstates->elapsed_time += time_diff;
+ freq_data.pstate_id = gpstates->last_lpstate;
+
+ if ((gpstates->last_gpstate == freq_data.pstate_id) ||
+ (gpstates->elapsed_time > MAX_RAMP_DOWN_TIME)) {
+ gpstate_id = freq_data.pstate_id;
+ reset_gpstates(policy);
+ gpstates->highest_lpstate = freq_data.pstate_id;
+ } else {
+ gpstate_id = calc_global_pstate(gpstates->elapsed_time,
+ gpstates->highest_lpstate,
+ freq_data.pstate_id);
+ }
+
+ /*
+ * If local pstate is equal to global pstate, rampdown is over
+ * So timer is not required to be queued.
+ */
+ if (gpstate_id != freq_data.pstate_id)
+ queue_gpstate_timer(gpstates);
+
+ freq_data.gpstate_id = gpstate_id;
+ gpstates->last_gpstate = freq_data.gpstate_id;
+ gpstates->last_lpstate = freq_data.pstate_id;
+
+ /* Timer may get migrated to a different cpu on cpu hot unplug */
+ smp_call_function_any(policy->cpus, set_pstate, &freq_data, 1);
+ spin_unlock(&gpstates->gpstate_lock);
+}
+
/*
* powernv_cpufreq_target_index: Sets the frequency corresponding to
* the cpufreq table entry indexed by new_index on the cpus in the
@@ -433,6 +595,9 @@ static int powernv_cpufreq_target_index(struct cpufreq_policy *policy,
unsigned int new_index)
{
struct powernv_smp_call_data freq_data;
+ unsigned int cur_msec, gpstate_id;
+ unsigned long flags;
+ struct global_pstate_info *gpstates = policy->driver_data;
if (unlikely(rebooting) && new_index != get_nominal_index())
return 0;
@@ -440,22 +605,70 @@ static int powernv_cpufreq_target_index(struct cpufreq_policy *policy,
if (!throttled)
powernv_cpufreq_throttle_check(NULL);
+ cur_msec = jiffies_to_msecs(get_jiffies_64());
+
+ spin_lock_irqsave(&gpstates->gpstate_lock, flags);
freq_data.pstate_id = powernv_freqs[new_index].driver_data;
+ if (!gpstates->last_sampled_time) {
+ gpstate_id = freq_data.pstate_id;
+ gpstates->highest_lpstate = freq_data.pstate_id;
+ goto gpstates_done;
+ }
+
+ if (gpstates->last_gpstate > freq_data.pstate_id) {
+ gpstates->elapsed_time += cur_msec -
+ gpstates->last_sampled_time;
+
+ /*
+ * If its has been ramping down for more than MAX_RAMP_DOWN_TIME
+ * we should be resetting all global pstate related data. Set it
+ * equal to local pstate to start fresh.
+ */
+ if (gpstates->elapsed_time > MAX_RAMP_DOWN_TIME) {
+ reset_gpstates(policy);
+ gpstates->highest_lpstate = freq_data.pstate_id;
+ gpstate_id = freq_data.pstate_id;
+ } else {
+ /* Elaspsed_time is less than 5 seconds, continue to rampdown */
+ gpstate_id = calc_global_pstate(gpstates->elapsed_time,
+ gpstates->highest_lpstate,
+ freq_data.pstate_id);
+ }
+ } else {
+ reset_gpstates(policy);
+ gpstates->highest_lpstate = freq_data.pstate_id;
+ gpstate_id = freq_data.pstate_id;
+ }
+
+ /*
+ * If local pstate is equal to global pstate, rampdown is over
+ * So timer is not required to be queued.
+ */
+ if (gpstate_id != freq_data.pstate_id)
+ queue_gpstate_timer(gpstates);
+
+gpstates_done:
+ freq_data.gpstate_id = gpstate_id;
+ gpstates->last_sampled_time = cur_msec;
+ gpstates->last_gpstate = freq_data.gpstate_id;
+ gpstates->last_lpstate = freq_data.pstate_id;
+
/*
* Use smp_call_function to send IPI and execute the
* mtspr on target CPU. We could do that without IPI
* if current CPU is within policy->cpus (core)
*/
smp_call_function_any(policy->cpus, set_pstate, &freq_data, 1);
-
+ spin_unlock_irqrestore(&gpstates->gpstate_lock, flags);
return 0;
}
static int powernv_cpufreq_cpu_init(struct cpufreq_policy *policy)
{
- int base, i;
+ int base, i, ret;
struct kernfs_node *kn;
+ struct global_pstate_info *gpstates;
base = cpu_first_thread_sibling(policy->cpu);
@@ -475,7 +688,34 @@ static int powernv_cpufreq_cpu_init(struct cpufreq_policy *policy)
} else {
kernfs_put(kn);
}
- return cpufreq_table_validate_and_show(policy, powernv_freqs);
+
+ gpstates = kzalloc(sizeof(*gpstates), GFP_KERNEL);
+ if (!gpstates)
+ return -ENOMEM;
+
+ policy->driver_data = gpstates;
+
+ /* initialize timer */
+ init_timer_deferrable(&gpstates->timer);
+ gpstates->timer.data = (unsigned long)policy;
+ gpstates->timer.function = gpstate_timer_handler;
+ gpstates->timer.expires = jiffies +
+ msecs_to_jiffies(GPSTATE_TIMER_INTERVAL);
+ spin_lock_init(&gpstates->gpstate_lock);
+ ret = cpufreq_table_validate_and_show(policy, powernv_freqs);
+
+ if (ret < 0)
+ kfree(policy->driver_data);
+
+ return ret;
+}
+
+static int powernv_cpufreq_cpu_exit(struct cpufreq_policy *policy)
+{
+ /* timer is deleted in cpufreq_cpu_stop() */
+ kfree(policy->driver_data);
+
+ return 0;
}
static int powernv_cpufreq_reboot_notifier(struct notifier_block *nb,
@@ -603,15 +843,19 @@ static struct notifier_block powernv_cpufreq_opal_nb = {
static void powernv_cpufreq_stop_cpu(struct cpufreq_policy *policy)
{
struct powernv_smp_call_data freq_data;
+ struct global_pstate_info *gpstates = policy->driver_data;
freq_data.pstate_id = powernv_pstate_info.min;
+ freq_data.gpstate_id = powernv_pstate_info.min;
smp_call_function_single(policy->cpu, set_pstate, &freq_data, 1);
+ del_timer_sync(&gpstates->timer);
}
static struct cpufreq_driver powernv_cpufreq_driver = {
.name = "powernv-cpufreq",
.flags = CPUFREQ_CONST_LOOPS,
.init = powernv_cpufreq_cpu_init,
+ .exit = powernv_cpufreq_cpu_exit,
.verify = cpufreq_generic_frequency_table_verify,
.target_index = powernv_cpufreq_target_index,
.get = powernv_cpufreq_get,
--
2.5.5