* [PATCH 1/1] intel_pstate: Increase hold-off time before samples are scaled v2
@ 2016-02-23 14:29 Mel Gorman
2016-02-23 14:48 ` kbuild test robot
2016-02-23 21:50 ` Srinivas Pandruvada
0 siblings, 2 replies; 6+ messages in thread
From: Mel Gorman @ 2016-02-23 14:29 UTC (permalink / raw)
To: Rafael Wysocki
Cc: Doug Smythies, Stephane Gasparini, Srinivas Pandruvada,
Dirk Brandewie, Ingo Molnar, Peter Zijlstra, Matt Fleming,
Mike Galbraith, Linux-PM, LKML, Mel Gorman
Added a suggested change from Doug Smythies and can add a Signed-off-by
if Doug is ok with that.
Changelog since v1
o Remove divide that is likely unnecessary (dsmythies)
o Rebase on top of linux-pm/linux-next
The PID relies on samples of equal time but this does not apply for
deferrable timers when the CPU is idle. intel_pstate checks if the actual
duration between samples is large and if so, the "busyness" of the CPU
is scaled.
This assumes the delay was a deferred timer but a workload may simply have
been idle for a short time if it's context switching between a server and
client or waiting very briefly on IO. It's compounded by the problem that
server/clients migrate between CPUs due to wake-affine trying to maximise
hot cache usage. In such cases, the cores are not considered busy and the
frequency is dropped prematurely.
This patch increases the hold-off value before the busyness is scaled. It
was selected based simply on testing until the desired result was found.
Tests were conducted with workloads that are either client/server based
or short-lived IO.
dbench4
4.5.0-rc4 4.5.0-rc4
pmnext-20160219 sample-v2r3
Hmean mb/sec-1 322.84 ( 0.00%) 322.40 ( -0.14%)
Hmean mb/sec-2 604.32 ( 0.00%) 615.03 ( 1.77%)
Hmean mb/sec-4 680.53 ( 0.00%) 707.78 ( 4.00%)
Hmean mb/sec-8 705.40 ( 0.00%) 742.36 ( 5.24%)
4.5.0-rc4 4.5.0-rc4
pmnext-20160219 sample-v2r3
User 1483.79 1393.30
System 3847.87 3652.56
Elapsed 5406.79 5405.82
4.5.0-rc4 4.5.0-rc4
pmnext-20160219 sample-v2r3
Mean %Busy 27.59 26.21
Mean CPU%c1 43.37 44.21
Mean CPU%c3 7.30 7.67
Mean CPU%c6 21.74 21.91
Mean CPU%c7 0.00 0.00
Mean CorWatt 4.69 5.11
Mean PkgWatt 6.92 7.34
There performance boost is marginal but the system CPU usage is much reduced and overall the
impact on power usage is marginal.
iozone for small files and varying block sizes. Format is IOOperation-filessize-recordsize
4.5.0-rc2 4.5.0-rc2
vanilla sample-v1r1
Hmean SeqWrite-200704-1 745153.35 ( 0.00%) 835705.87 ( 12.15%)
Hmean SeqWrite-200704-2 1073584.72 ( 0.00%) 1181464.54 ( 10.05%)
Hmean SeqWrite-200704-4 1470279.09 ( 0.00%) 1800606.95 ( 22.47%)
Hmean SeqWrite-200704-8 1557199.39 ( 0.00%) 1858933.62 ( 19.38%)
Hmean SeqWrite-200704-16 1604615.45 ( 0.00%) 1982299.77 ( 23.54%)
Hmean SeqWrite-200704-32 1651599.28 ( 0.00%) 1896837.26 ( 14.85%)
Hmean SeqWrite-200704-64 1666177.22 ( 0.00%) 2061195.61 ( 23.71%)
Hmean SeqWrite-200704-128 1669019.85 ( 0.00%) 1940620.93 ( 16.27%)
Hmean SeqWrite-200704-256 1657685.15 ( 0.00%) 2054770.87 ( 23.95%)
Hmean SeqWrite-200704-512 1657502.45 ( 0.00%) 2064537.12 ( 24.56%)
Hmean SeqWrite-200704-1024 1658418.19 ( 0.00%) 2065680.07 ( 24.56%)
Hmean SeqWrite-401408-1 823115.74 ( 0.00%) 873454.97 ( 6.12%)
Hmean SeqWrite-401408-2 1175839.58 ( 0.00%) 1380834.12 ( 17.43%)
Hmean SeqWrite-401408-4 1746819.22 ( 0.00%) 1959568.79 ( 12.18%)
Hmean SeqWrite-401408-8 1857904.68 ( 0.00%) 2119305.42 ( 14.07%)
Hmean SeqWrite-401408-16 1883956.56 ( 0.00%) 2263314.65 ( 20.14%)
Hmean SeqWrite-401408-32 1928933.02 ( 0.00%) 2359131.00 ( 22.30%)
Hmean SeqWrite-401408-64 1947503.44 ( 0.00%) 2269170.03 ( 16.52%)
Hmean SeqWrite-401408-128 1963530.81 ( 0.00%) 2360367.91 ( 20.21%)
Hmean SeqWrite-401408-256 1930490.52 ( 0.00%) 2179920.99 ( 12.92%)
Hmean SeqWrite-401408-512 1944400.52 ( 0.00%) 2268039.39 ( 16.64%)
Hmean SeqWrite-401408-1024 1930551.06 ( 0.00%) 2294266.42 ( 18.84%)
Hmean Rewrite-200704-1 1157432.45 ( 0.00%) 1161993.50 ( 0.39%)
Hmean Rewrite-200704-2 1769952.94 ( 0.00%) 1875955.03 ( 5.99%)
Hmean Rewrite-200704-4 2534237.50 ( 0.00%) 2850813.95 ( 12.49%)
Hmean Rewrite-200704-8 2739338.32 ( 0.00%) 3069949.91 ( 12.07%)
Hmean Rewrite-200704-16 2869980.18 ( 0.00%) 3084573.49 ( 7.48%)
Hmean Rewrite-200704-32 2893382.66 ( 0.00%) 3125994.45 ( 8.04%)
Hmean Rewrite-200704-64 2971476.80 ( 0.00%) 3037778.64 ( 2.23%)
Hmean Rewrite-200704-128 2899499.67 ( 0.00%) 3061961.77 ( 5.60%)
Hmean Rewrite-200704-256 2931964.78 ( 0.00%) 3047588.38 ( 3.94%)
Hmean Rewrite-200704-512 2905287.39 ( 0.00%) 2716185.78 ( -6.51%)
Hmean Rewrite-200704-1024 2852964.56 ( 0.00%) 2979784.30 ( 4.45%)
Hmean Rewrite-401408-1 1340119.25 ( 0.00%) 1367559.86 ( 2.05%)
Hmean Rewrite-401408-2 2066152.00 ( 0.00%) 2150180.25 ( 4.07%)
Hmean Rewrite-401408-4 2877697.54 ( 0.00%) 3141556.92 ( 9.17%)
Hmean Rewrite-401408-8 3111565.24 ( 0.00%) 3351724.68 ( 7.72%)
Hmean Rewrite-401408-16 3121552.56 ( 0.00%) 3460645.54 ( 10.86%)
Hmean Rewrite-401408-32 3156754.87 ( 0.00%) 3689350.17 ( 16.87%)
Hmean Rewrite-401408-64 3323557.00 ( 0.00%) 3476782.18 ( 4.61%)
Hmean Rewrite-401408-128 3402701.75 ( 0.00%) 3530951.84 ( 3.77%)
Hmean Rewrite-401408-256 3204914.57 ( 0.00%) 3277704.44 ( 2.27%)
Hmean Rewrite-401408-512 3133442.60 ( 0.00%) 3387768.91 ( 8.12%)
Hmean Rewrite-401408-1024 3143721.63 ( 0.00%) 3341908.51 ( 6.30%)
4.5.0-rc4 4.5.0-rc4
pmnext-20160219 sample-v2r3
Mean %Busy 3.45 3.32
Mean CPU%c1 5.44 6.01
Mean CPU%c3 0.13 0.09
Mean CPU%c6 90.98 90.58
Mean CPU%c7 0.00 0.00
Mean CorWatt 1.75 1.83
Mean PkgWatt 3.92 3.98
Max %Busy 16.46 16.46
Max CPU%c1 17.33 17.60
Max CPU%c3 1.62 1.42
Max CPU%c6 96.10 95.43
Max CPU%c7 0.00 0.00
Max CorWatt 5.47 5.54
Max PkgWatt 7.60 7.63
The other operations are omitted as they showed either no or negligible performance difference.
For sequential writes and rewrites there is a massive gain in throughput
for very small files. The increase in power consumption is negligible.
It is known that the increase is not universal. Larger core machines see
a much smaller benefit so the rate of CPU migrations are a factor.
In all cases, there are some CPU migrations because wakers pull wakees
to nearby CPUs. It could be argued that such workloads should be pinned
but this puts a burden on the user that may not even be possible in all
cases. The scheduler could try keeping processes on the same CPUs but that
would impact cache hotness and cause a different class of issues. It is
inevitable that there will be some conflict between power management and
scheduling decisions but there is some gains from delaying idling slightly
without a severe impact on power consumption.
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
drivers/cpufreq/intel_pstate.c | 16 +++++++---------
1 file changed, 7 insertions(+), 9 deletions(-)
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index f4d85c2ae7b1..6f3bf1e68f63 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -975,17 +975,15 @@ static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu)
/*
* Since our utilization update callback will not run unless we are
- * in C0, check if the actual elapsed time is significantly greater (3x)
- * than our sample interval. If it is, then we were idle for a long
- * enough period of time to adjust our busyness.
+ * in C0, check if the actual elapsed time is significantly greater (12x)
+ * than our sample interval. If it is, then assume we were idle for a long
+ * enough period of time to adjust our busyness. While the assumption
+ * is not always true, it seems to be good enough.
*/
duration_ns = cpu->sample.time - cpu->last_sample_time;
- if ((s64)duration_ns > pid_params.sample_rate_ns * 3
- && cpu->last_sample_time > 0) {
- sample_ratio = div_fp(int_tofp(pid_params.sample_rate_ns),
- int_tofp(duration_ns));
- core_busy = mul_fp(core_busy, sample_ratio);
- }
+ if ((s64)duration_ns > pid_params.sample_rate_ns * 12
+ && cpu->last_sample_time > 0)
+ core_busy = 0;
cpu->sample.busy_scaled = core_busy;
return cpu->pstate.current_pstate - pid_calc(&cpu->pid, core_busy);
--
2.6.4
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH 1/1] intel_pstate: Increase hold-off time before samples are scaled v2
2016-02-23 14:29 [PATCH 1/1] intel_pstate: Increase hold-off time before samples are scaled v2 Mel Gorman
@ 2016-02-23 14:48 ` kbuild test robot
2016-02-23 21:50 ` Srinivas Pandruvada
1 sibling, 0 replies; 6+ messages in thread
From: kbuild test robot @ 2016-02-23 14:48 UTC (permalink / raw)
To: Mel Gorman
Cc: kbuild-all, Rafael Wysocki, Doug Smythies, Stephane Gasparini,
Srinivas Pandruvada, Dirk Brandewie, Ingo Molnar, Peter Zijlstra,
Matt Fleming, Mike Galbraith, Linux-PM, LKML, Mel Gorman
[-- Attachment #1: Type: text/plain, Size: 3436 bytes --]
Hi Mel,
[auto build test WARNING on pm/linux-next]
[also build test WARNING on next-20160223]
[cannot apply to v4.5-rc5]
[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]
url: https://github.com/0day-ci/linux/commits/Mel-Gorman/intel_pstate-Increase-hold-off-time-before-samples-are-scaled-v2/20160223-223212
base: https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git linux-next
config: i386-randconfig-x006-201608 (attached as .config)
reproduce:
# save the attached .config to linux build tree
make ARCH=i386
All warnings (new ones prefixed by >>):
drivers/cpufreq/intel_pstate.c: In function 'get_target_pstate_use_performance':
>> drivers/cpufreq/intel_pstate.c:957:49: warning: unused variable 'sample_ratio' [-Wunused-variable]
int32_t core_busy, max_pstate, current_pstate, sample_ratio;
^
vim +/sample_ratio +957 drivers/cpufreq/intel_pstate.c
63d1d656 Philippe Longepe 2015-12-04 941
63d1d656 Philippe Longepe 2015-12-04 942
e70eed2b Philippe Longepe 2015-12-04 943 /*
e70eed2b Philippe Longepe 2015-12-04 944 * The load can be estimated as the ratio of the mperf counter
e70eed2b Philippe Longepe 2015-12-04 945 * running at a constant frequency during active periods
e70eed2b Philippe Longepe 2015-12-04 946 * (C0) and the time stamp counter running at the same frequency
e70eed2b Philippe Longepe 2015-12-04 947 * also during C-states.
e70eed2b Philippe Longepe 2015-12-04 948 */
63d1d656 Philippe Longepe 2015-12-04 949 cpu_load = div64_u64(int_tofp(100) * mperf, sample->tsc);
e70eed2b Philippe Longepe 2015-12-04 950 cpu->sample.busy_scaled = cpu_load;
e70eed2b Philippe Longepe 2015-12-04 951
e70eed2b Philippe Longepe 2015-12-04 952 return cpu->pstate.current_pstate - pid_calc(&cpu->pid, cpu_load);
e70eed2b Philippe Longepe 2015-12-04 953 }
e70eed2b Philippe Longepe 2015-12-04 954
157386b6 Philippe Longepe 2015-12-04 955 static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu)
93f0822d Dirk Brandewie 2013-02-06 956 {
c4ee841f Dirk Brandewie 2014-05-29 @957 int32_t core_busy, max_pstate, current_pstate, sample_ratio;
402c43ed Rafael J. Wysocki 2016-02-05 958 u64 duration_ns;
93f0822d Dirk Brandewie 2013-02-06 959
e0d4c8f8 Kristen Carlson Accardi 2014-12-10 960 /*
e0d4c8f8 Kristen Carlson Accardi 2014-12-10 961 * core_busy is the ratio of actual performance to max
e0d4c8f8 Kristen Carlson Accardi 2014-12-10 962 * max_pstate is the max non turbo pstate available
e0d4c8f8 Kristen Carlson Accardi 2014-12-10 963 * current_pstate was the pstate that was requested during
e0d4c8f8 Kristen Carlson Accardi 2014-12-10 964 * the last sample period.
e0d4c8f8 Kristen Carlson Accardi 2014-12-10 965 *
:::::: The code at line 957 was first introduced by commit
:::::: c4ee841f602e5eef8eab673295c49c5b49d7732b intel_pstate: add sample time scaling
:::::: TO: Dirk Brandewie <dirk.j.brandewie@intel.com>
:::::: CC: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
[-- Attachment #2: .config.gz --]
[-- Type: application/octet-stream, Size: 23263 bytes --]
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH 1/1] intel_pstate: Increase hold-off time before samples are scaled v2
@ 2016-02-23 14:48 ` kbuild test robot
0 siblings, 0 replies; 6+ messages in thread
From: kbuild test robot @ 2016-02-23 14:48 UTC (permalink / raw)
Cc: kbuild-all, Rafael Wysocki, Doug Smythies, Stephane Gasparini,
Srinivas Pandruvada, Dirk Brandewie, Ingo Molnar, Peter Zijlstra,
Matt Fleming, Mike Galbraith, Linux-PM, LKML, Mel Gorman
[-- Attachment #1: Type: text/plain, Size: 3436 bytes --]
Hi Mel,
[auto build test WARNING on pm/linux-next]
[also build test WARNING on next-20160223]
[cannot apply to v4.5-rc5]
[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]
url: https://github.com/0day-ci/linux/commits/Mel-Gorman/intel_pstate-Increase-hold-off-time-before-samples-are-scaled-v2/20160223-223212
base: https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git linux-next
config: i386-randconfig-x006-201608 (attached as .config)
reproduce:
# save the attached .config to linux build tree
make ARCH=i386
All warnings (new ones prefixed by >>):
drivers/cpufreq/intel_pstate.c: In function 'get_target_pstate_use_performance':
>> drivers/cpufreq/intel_pstate.c:957:49: warning: unused variable 'sample_ratio' [-Wunused-variable]
int32_t core_busy, max_pstate, current_pstate, sample_ratio;
^
vim +/sample_ratio +957 drivers/cpufreq/intel_pstate.c
63d1d656 Philippe Longepe 2015-12-04 941
63d1d656 Philippe Longepe 2015-12-04 942
e70eed2b Philippe Longepe 2015-12-04 943 /*
e70eed2b Philippe Longepe 2015-12-04 944 * The load can be estimated as the ratio of the mperf counter
e70eed2b Philippe Longepe 2015-12-04 945 * running at a constant frequency during active periods
e70eed2b Philippe Longepe 2015-12-04 946 * (C0) and the time stamp counter running at the same frequency
e70eed2b Philippe Longepe 2015-12-04 947 * also during C-states.
e70eed2b Philippe Longepe 2015-12-04 948 */
63d1d656 Philippe Longepe 2015-12-04 949 cpu_load = div64_u64(int_tofp(100) * mperf, sample->tsc);
e70eed2b Philippe Longepe 2015-12-04 950 cpu->sample.busy_scaled = cpu_load;
e70eed2b Philippe Longepe 2015-12-04 951
e70eed2b Philippe Longepe 2015-12-04 952 return cpu->pstate.current_pstate - pid_calc(&cpu->pid, cpu_load);
e70eed2b Philippe Longepe 2015-12-04 953 }
e70eed2b Philippe Longepe 2015-12-04 954
157386b6 Philippe Longepe 2015-12-04 955 static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu)
93f0822d Dirk Brandewie 2013-02-06 956 {
c4ee841f Dirk Brandewie 2014-05-29 @957 int32_t core_busy, max_pstate, current_pstate, sample_ratio;
402c43ed Rafael J. Wysocki 2016-02-05 958 u64 duration_ns;
93f0822d Dirk Brandewie 2013-02-06 959
e0d4c8f8 Kristen Carlson Accardi 2014-12-10 960 /*
e0d4c8f8 Kristen Carlson Accardi 2014-12-10 961 * core_busy is the ratio of actual performance to max
e0d4c8f8 Kristen Carlson Accardi 2014-12-10 962 * max_pstate is the max non turbo pstate available
e0d4c8f8 Kristen Carlson Accardi 2014-12-10 963 * current_pstate was the pstate that was requested during
e0d4c8f8 Kristen Carlson Accardi 2014-12-10 964 * the last sample period.
e0d4c8f8 Kristen Carlson Accardi 2014-12-10 965 *
:::::: The code at line 957 was first introduced by commit
:::::: c4ee841f602e5eef8eab673295c49c5b49d7732b intel_pstate: add sample time scaling
:::::: TO: Dirk Brandewie <dirk.j.brandewie@intel.com>
:::::: CC: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
[-- Attachment #2: .config.gz --]
[-- Type: application/octet-stream, Size: 23263 bytes --]
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 1/1] intel_pstate: Increase hold-off time before samples are scaled v2
2016-02-23 14:29 [PATCH 1/1] intel_pstate: Increase hold-off time before samples are scaled v2 Mel Gorman
2016-02-23 14:48 ` kbuild test robot
@ 2016-02-23 21:50 ` Srinivas Pandruvada
2016-02-24 9:03 ` Mel Gorman
1 sibling, 1 reply; 6+ messages in thread
From: Srinivas Pandruvada @ 2016-02-23 21:50 UTC (permalink / raw)
To: Mel Gorman, Rafael Wysocki
Cc: Doug Smythies, Stephane Gasparini, Dirk Brandewie, Ingo Molnar,
Peter Zijlstra, Matt Fleming, Mike Galbraith, Linux-PM, LKML
[-- Attachment #1: Type: text/plain, Size: 1491 bytes --]
On Tue, 2016-02-23 at 14:29 +0000, Mel Gorman wrote:
> Added a suggested change from Doug Smythies and can add a Signed-off-
> by
> if Doug is ok with that.
>
> Changelog since v1
> o Remove divide that is likely unnecessary (ds
> mythies)
> o Rebase on top of linux-pm/linux-next
>
> The PID relies on samples of equal time but this does not apply for
> deferrable timers when the CPU is idle. intel_pstate checks if the
> actual
> duration between samples is large and if so, the "busyness" of the
> CPU
> is scaled.
>
> This assumes the delay was a deferred timer but a workload may simply
> have
> been idle for a short time if it's context switching between a server
> and
> client or waiting very briefly on IO. It's compounded by the problem
> that
> server/clients migrate between CPUs due to wake-affine trying to
> maximise
> hot cache usage. In such cases, the cores are not considered busy and
> the
> frequency is dropped prematurely.
>
> This patch increases the hold-off value before the busyness is
> scaled. It
> was selected based simply on testing until the desired result was
> found.
> Tests were conducted with workloads that are either client/server
> based
> or short-lived IO.
Attached specpower comparison for Haswell EP Grantley server.
This workload ran about an hour+.
Difference in OPS:
+1019
Difference in power:
+308.6
Difference in perf/watt -312.479023
So we are consuming 308 Watts on average for doing 1019 operation more.
Thanks,
Srinivas
[-- Attachment #2: HSW Grantley (hswep) spec_power (02_23_16).pdf --]
[-- Type: application/pdf, Size: 36086 bytes --]
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 1/1] intel_pstate: Increase hold-off time before samples are scaled v2
2016-02-23 21:50 ` Srinivas Pandruvada
@ 2016-02-24 9:03 ` Mel Gorman
2016-02-24 13:33 ` Rafael J. Wysocki
0 siblings, 1 reply; 6+ messages in thread
From: Mel Gorman @ 2016-02-24 9:03 UTC (permalink / raw)
To: Srinivas Pandruvada
Cc: Rafael Wysocki, Doug Smythies, Stephane Gasparini,
Dirk Brandewie, Ingo Molnar, Peter Zijlstra, Matt Fleming,
Mike Galbraith, Linux-PM, LKML
On Tue, Feb 23, 2016 at 01:50:34PM -0800, Srinivas Pandruvada wrote:
> On Tue, 2016-02-23 at 14:29 +0000, Mel Gorman wrote:
> > Added a suggested change from Doug Smythies and can add a Signed-off-
> > by
> > if Doug is ok with that.
> >
> > Changelog since v1
> > o Remove divide that is likely unnecessary (ds
> > mythies)
> > o Rebase on top of linux-pm/linux-next
> >
> > The PID relies on samples of equal time but this does not apply for
> > deferrable timers when the CPU is idle. intel_pstate checks if the
> > actual
> > duration between samples is large and if so, the "busyness" of the
> > CPU
> > is scaled.
> >
> > This assumes the delay was a deferred timer but a workload may simply
> > have
> > been idle for a short time if it's context switching between a server
> > and
> > client or waiting very briefly on IO. It's compounded by the problem
> > that
> > server/clients migrate between CPUs due to wake-affine trying to
> > maximise
> > hot cache usage. In such cases, the cores are not considered busy and
> > the
> > frequency is dropped prematurely.
> >
> > This patch increases the hold-off value before the busyness is
> > scaled. It
> > was selected based simply on testing until the desired result was
> > found.
> > Tests were conducted with workloads that are either client/server
> > based
> > or short-lived IO.
>
> Attached specpower comparison for Haswell EP Grantley server.
>
So this looks like a bust in terms of specpower. It is incredibly
unfortunate though. There are basic workloads that are simply performing
way below what the CPU is capable of unless the user is either willing
to tune power management or pin tasks to CPUs and hope for the best.
Ideally we want to reduce those forum postings that suggest disabling
intel_pstate entirely or setting performance.
Given that I'm very weak in the intel_pstate driver in general and was
relying on bisection to find problem commits, are there any others with
"have your cake and eat it twice" options? Ideally it would restore
performance to simple client/server workloads and ones that idle briefly
on IO without getting red flagged by specpower.
--
Mel Gorman
SUSE Labs
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 1/1] intel_pstate: Increase hold-off time before samples are scaled v2
2016-02-24 9:03 ` Mel Gorman
@ 2016-02-24 13:33 ` Rafael J. Wysocki
0 siblings, 0 replies; 6+ messages in thread
From: Rafael J. Wysocki @ 2016-02-24 13:33 UTC (permalink / raw)
To: Mel Gorman
Cc: Srinivas Pandruvada, Doug Smythies, Stephane Gasparini,
Dirk Brandewie, Ingo Molnar, Peter Zijlstra, Matt Fleming,
Mike Galbraith, Linux-PM, LKML
On Wednesday, February 24, 2016 09:03:01 AM Mel Gorman wrote:
> On Tue, Feb 23, 2016 at 01:50:34PM -0800, Srinivas Pandruvada wrote:
> > On Tue, 2016-02-23 at 14:29 +0000, Mel Gorman wrote:
> > > Added a suggested change from Doug Smythies and can add a Signed-off-
> > > by
> > > if Doug is ok with that.
> > >
> > > Changelog since v1
> > > o Remove divide that is likely unnecessary (ds
> > > mythies)
> > > o Rebase on top of linux-pm/linux-next
> > >
> > > The PID relies on samples of equal time but this does not apply for
> > > deferrable timers when the CPU is idle. intel_pstate checks if the
> > > actual
> > > duration between samples is large and if so, the "busyness" of the
> > > CPU
> > > is scaled.
> > >
> > > This assumes the delay was a deferred timer but a workload may simply
> > > have
> > > been idle for a short time if it's context switching between a server
> > > and
> > > client or waiting very briefly on IO. It's compounded by the problem
> > > that
> > > server/clients migrate between CPUs due to wake-affine trying to
> > > maximise
> > > hot cache usage. In such cases, the cores are not considered busy and
> > > the
> > > frequency is dropped prematurely.
> > >
> > > This patch increases the hold-off value before the busyness is
> > > scaled. It
> > > was selected based simply on testing until the desired result was
> > > found.
> > > Tests were conducted with workloads that are either client/server
> > > based
> > > or short-lived IO.
> >
> > Attached specpower comparison for Haswell EP Grantley server.
> >
>
> So this looks like a bust in terms of specpower. It is incredibly
> unfortunate though. There are basic workloads that are simply performing
> way below what the CPU is capable of unless the user is either willing
> to tune power management or pin tasks to CPUs and hope for the best.
> Ideally we want to reduce those forum postings that suggest disabling
> intel_pstate entirely or setting performance.
>
> Given that I'm very weak in the intel_pstate driver in general and was
> relying on bisection to find problem commits, are there any others with
> "have your cake and eat it twice" options? Ideally it would restore
> performance to simple client/server workloads and ones that idle briefly
> on IO without getting red flagged by specpower.
Srinivas is working on using utilization data from the scheduler in
intel_pstate, which I think is the way to go to improve performance.
For example, we may react to increases in utilization reported by the
scheduler by ramping up the P-state more aggressivly and similar. Since
we're now going to get the utilization numbers as soon as they become
available, we should be able to react changes in them right away.
Thanks,
Rafael
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2016-02-24 13:32 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-02-23 14:29 [PATCH 1/1] intel_pstate: Increase hold-off time before samples are scaled v2 Mel Gorman
2016-02-23 14:48 ` kbuild test robot
2016-02-23 14:48 ` kbuild test robot
2016-02-23 21:50 ` Srinivas Pandruvada
2016-02-24 9:03 ` Mel Gorman
2016-02-24 13:33 ` Rafael J. Wysocki
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