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Groups > linux.kernel > #1603976 > unrolled thread
| Started by | "Rafael J. Wysocki" <rjw@rjwysocki.net> |
|---|---|
| First post | 2017-03-19 14:50 +0100 |
| Last post | 2017-03-27 09:20 +0200 |
| Articles | 3 on this page of 63 — 8 participants |
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[PATCH 0/2] cpufreq: schedutil: Fix and optimization "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-19 14:50 +0100
[PATCH 1/2] cpufreq: schedutil: Fix per-CPU structure initialization in sugov_start() "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-19 14:50 +0100
Re: [PATCH 1/2] cpufreq: schedutil: Fix per-CPU structure initialization in sugov_start() Viresh Kumar <viresh.kumar@linaro.org> - 2017-03-20 04:30 +0100
Re: [PATCH 1/2] cpufreq: schedutil: Fix per-CPU structure initialization in sugov_start() "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 13:50 +0100
[RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-19 14:50 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-19 22:40 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-19 22:50 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-20 12:10 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 13:50 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Viresh Kumar <viresh.kumar@linaro.org> - 2017-03-20 05:00 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-20 09:30 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-20 13:40 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Joel Fernandes <joelaf@google.com> - 2017-03-23 01:00 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-23 23:10 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Joel Fernandes <joelaf@google.com> - 2017-03-25 04:50 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-27 09:10 +0200
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 14:10 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-20 14:40 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 14:30 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-20 12:50 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 13:50 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-20 14:00 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-20 14:10 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 14:40 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-20 15:20 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 14:20 +0100
[RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 23:00 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Viresh Kumar <viresh.kumar@linaro.org> - 2017-03-21 07:50 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs "Rafael J. Wysocki" <rafael@kernel.org> - 2017-03-21 13:40 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-21 10:00 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-21 13:00 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-21 14:30 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-21 14:40 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-21 15:30 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-21 15:40 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-21 15:50 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-21 16:00 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-21 16:10 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-21 16:30 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-21 18:10 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-21 18:30 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-21 16:10 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-21 16:20 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-21 20:30 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-21 16:10 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-21 16:10 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-21 15:40 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-21 16:00 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-21 16:00 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-21 18:10 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-21 18:10 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-21 13:00 +0100
[RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-22 00:20 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Peter Zijlstra <peterz@infradead.org> - 2017-03-22 10:30 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Viresh Kumar <viresh.kumar@linaro.org> - 2017-03-22 11:10 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Joel Fernandes <joelaf@google.com> - 2017-03-23 02:10 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Sai Gurrappadi <sgurrappadi@nvidia.com> - 2017-03-23 20:30 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Sai Gurrappadi <sgurrappadi@nvidia.com> - 2017-03-23 22:00 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely "Rafael J. Wysocki" <rafael@kernel.org> - 2017-03-24 02:40 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Sai Gurrappadi <sgurrappadi@nvidia.com> - 2017-03-24 20:20 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Sai Gurrappadi <sgurrappadi@nvidia.com> - 2017-03-25 02:20 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely "Rafael J. Wysocki" <rafael@kernel.org> - 2017-03-25 02:40 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-27 09:20 +0200
Page 4 of 4 — ← Prev page 1 2 3 [4]
| From | Sai Gurrappadi <sgurrappadi@nvidia.com> |
|---|---|
| Date | 2017-03-25 02:20 +0100 |
| Subject | Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely |
| Message-ID | <toIx3-1Ip-1@gated-at.bofh.it> |
| In reply to | #1606069 |
Hi Rafael, On 03/21/2017 04:08 PM, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > The way the schedutil governor uses the PELT metric causes it to > underestimate the CPU utilization in some cases. > > That can be easily demonstrated by running kernel compilation on > a Sandy Bridge Intel processor, running turbostat in parallel with > it and looking at the values written to the MSR_IA32_PERF_CTL > register. Namely, the expected result would be that when all CPUs > were 100% busy, all of them would be requested to run in the maximum > P-state, but observation shows that this clearly isn't the case. > The CPUs run in the maximum P-state for a while and then are > requested to run slower and go back to the maximum P-state after > a while again. That causes the actual frequency of the processor to > visibly oscillate below the sustainable maximum in a jittery fashion > which clearly is not desirable. > > That has been attributed to CPU utilization metric updates on task > migration that cause the total utilization value for the CPU to be > reduced by the utilization of the migrated task. If that happens, > the schedutil governor may see a CPU utilization reduction and will > attempt to reduce the CPU frequency accordingly right away. That > may be premature, though, for example if the system is generally > busy and there are other runnable tasks waiting to be run on that > CPU already. > Thinking out loud a bit, I wonder if what you really want to do is basically: schedutil_cpu_util(cpu) = max(cpu_rq(cpu)->cfs.util_avg, total_cpu_util_avg); Where total_cpu_util_avg tracks the average utilization of the CPU itself over time (% of time the CPU was busy) in the same PELT like manner. The difference here is that it doesn't change instantaneously as tasks migrate in/out but it decays/accumulates just like the per-entity util_avgs. Over time, total_cpu_util_avg and cfs_rq(cpu)->util_avg will tend towards each other the lesser the amount of 'overlap' / overloading. Yes, the above metric would 'overestimate' in case all tasks have migrated away and we are left with an idle CPU. A fix for that could be to just use the PELT value like so: schedutil_cpu_util(cpu) = max(cpu_rq(cpu)->cfs.util_avg, idle_cpu(cpu) ? 0 : total_cpu_util_avg); Note that the problem described here in the commit message doesn't need fully runnable threads, it just needs two threads to execute in parallel on the same CPU for a period of time. I don't think looking at just idle_calls necessarily covers all cases. Thoughts? Thanks, -Sai
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| From | "Rafael J. Wysocki" <rafael@kernel.org> |
|---|---|
| Date | 2017-03-25 02:40 +0100 |
| Subject | Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely |
| Message-ID | <toIQp-1P9-3@gated-at.bofh.it> |
| In reply to | #1609054 |
On Sat, Mar 25, 2017 at 2:14 AM, Sai Gurrappadi <sgurrappadi@nvidia.com> wrote: > Hi Rafael, > > On 03/21/2017 04:08 PM, Rafael J. Wysocki wrote: >> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> >> >> The way the schedutil governor uses the PELT metric causes it to >> underestimate the CPU utilization in some cases. >> >> That can be easily demonstrated by running kernel compilation on >> a Sandy Bridge Intel processor, running turbostat in parallel with >> it and looking at the values written to the MSR_IA32_PERF_CTL >> register. Namely, the expected result would be that when all CPUs >> were 100% busy, all of them would be requested to run in the maximum >> P-state, but observation shows that this clearly isn't the case. >> The CPUs run in the maximum P-state for a while and then are >> requested to run slower and go back to the maximum P-state after >> a while again. That causes the actual frequency of the processor to >> visibly oscillate below the sustainable maximum in a jittery fashion >> which clearly is not desirable. >> >> That has been attributed to CPU utilization metric updates on task >> migration that cause the total utilization value for the CPU to be >> reduced by the utilization of the migrated task. If that happens, >> the schedutil governor may see a CPU utilization reduction and will >> attempt to reduce the CPU frequency accordingly right away. That >> may be premature, though, for example if the system is generally >> busy and there are other runnable tasks waiting to be run on that >> CPU already. >> > > Thinking out loud a bit, I wonder if what you really want to do is basically: > > schedutil_cpu_util(cpu) = max(cpu_rq(cpu)->cfs.util_avg, total_cpu_util_avg); > > Where total_cpu_util_avg tracks the average utilization of the CPU itself over time (% of time the CPU was busy) in the same PELT like manner. The difference here is that it doesn't change instantaneously as tasks migrate in/out but it decays/accumulates just like the per-entity util_avgs. > > Over time, total_cpu_util_avg and cfs_rq(cpu)->util_avg will tend towards each other the lesser the amount of 'overlap' / overloading. > > Yes, the above metric would 'overestimate' in case all tasks have migrated away and we are left with an idle CPU. A fix for that could be to just use the PELT value like so: > > schedutil_cpu_util(cpu) = max(cpu_rq(cpu)->cfs.util_avg, idle_cpu(cpu) ? 0 : total_cpu_util_avg); > > Note that the problem described here in the commit message doesn't need fully runnable threads, it just needs two threads to execute in parallel on the same CPU for a period of time. I don't think looking at just idle_calls necessarily covers all cases. > > Thoughts? Well, is the total_cpu_util_avg metric readily available? Thanks, Rafael
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| From | Vincent Guittot <vincent.guittot@linaro.org> |
|---|---|
| Date | 2017-03-27 09:20 +0200 |
| Subject | Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely |
| Message-ID | <tpx6y-4iG-11@gated-at.bofh.it> |
| In reply to | #1609054 |
On 25 March 2017 at 02:14, Sai Gurrappadi <sgurrappadi@nvidia.com> wrote: > Hi Rafael, > > On 03/21/2017 04:08 PM, Rafael J. Wysocki wrote: >> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> >> >> The way the schedutil governor uses the PELT metric causes it to >> underestimate the CPU utilization in some cases. >> >> That can be easily demonstrated by running kernel compilation on >> a Sandy Bridge Intel processor, running turbostat in parallel with >> it and looking at the values written to the MSR_IA32_PERF_CTL >> register. Namely, the expected result would be that when all CPUs >> were 100% busy, all of them would be requested to run in the maximum >> P-state, but observation shows that this clearly isn't the case. >> The CPUs run in the maximum P-state for a while and then are >> requested to run slower and go back to the maximum P-state after >> a while again. That causes the actual frequency of the processor to >> visibly oscillate below the sustainable maximum in a jittery fashion >> which clearly is not desirable. >> >> That has been attributed to CPU utilization metric updates on task >> migration that cause the total utilization value for the CPU to be >> reduced by the utilization of the migrated task. If that happens, >> the schedutil governor may see a CPU utilization reduction and will >> attempt to reduce the CPU frequency accordingly right away. That >> may be premature, though, for example if the system is generally >> busy and there are other runnable tasks waiting to be run on that >> CPU already. >> > > Thinking out loud a bit, I wonder if what you really want to do is basically: > > schedutil_cpu_util(cpu) = max(cpu_rq(cpu)->cfs.util_avg, total_cpu_util_avg); > > Where total_cpu_util_avg tracks the average utilization of the CPU itself over time (% of time the CPU was busy) in the same PELT like manner. The difference here is that it doesn't change instantaneously as tasks migrate in/out but it decays/accumulates just like the per-entity util_avgs. But we loose the interest of immediate decrease when tasks migrate. Instead of total_cpu_util_avg we should better track RT utilization in the same manner so with ongoing work for deadline we will have : total_utilization = cfs.util_avg + rt's util_avg + deadline's util avg and we still take advantage of task migration effect > > Over time, total_cpu_util_avg and cfs_rq(cpu)->util_avg will tend towards each other the lesser the amount of 'overlap' / overloading. > > Yes, the above metric would 'overestimate' in case all tasks have migrated away and we are left with an idle CPU. A fix for that could be to just use the PELT value like so: > > schedutil_cpu_util(cpu) = max(cpu_rq(cpu)->cfs.util_avg, idle_cpu(cpu) ? 0 : total_cpu_util_avg); > > Note that the problem described here in the commit message doesn't need fully runnable threads, it just needs two threads to execute in parallel on the same CPU for a period of time. I don't think looking at just idle_calls necessarily covers all cases. > > Thoughts? > > Thanks, > -Sai
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