How are cpu.cfs_ period_us defined in cgroups and kernel.sched_cfs_bandwidth_slice_us related?
I've been trying to understand how the Completely Fair Scheduler in the Linux kernel does CPU bandwidth control.
After many readings, I still cannot wrap my head around how the CFS allows for each cgroup to define its own CFS period and how that ties in to the kernel.sched_cfs_bandwidth_slice_us sysctl setting.
Example A:
On a single CPU machine and there are two cgroups with different CFS periods defined. The quotas of each cgroup represent 50% of CPU time, totalling 100%.
cgroup-A: cpu.cfs_period_us=100ms
cpu.cfs_quota_us=50ms
cgroup-B: cpu.cfs_period_us=1000ms
cpu.cfs_quota_us=500ms
If each cgroup has a single process running, how are these processes scheduled given the CFS period (assuming both processes constantly require CPU time)?
Example B: What happens when cgroup-B have a higher quota than what's actually physically possible to fulfill, ie. cgroup-B set a 90% of the CPU time, and cgroup-A continues to set a quota to be 50% of the CPU time.
cgroup-A: cpu.cfs_period_us=100ms
cpu.cfs_quota_us=50ms
cgroup-B: cpu.cfs_period_us=1000ms
cpu.cfs_quota_us=900ms
How would CFS schedule the processes in this case when the quota is oversubscribed?
Thanks!
linux-kernel cgroups
asked 13 mins ago
Otto YiuOtto Yiu
61
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I've been trying to understand how the Completely Fair Scheduler in the Linux kernel does CPU bandwidth control.
After many readings, I still cannot wrap my head around how the CFS allows for each cgroup to define its own CFS period and how that ties in to the kernel.sched_cfs_bandwidth_slice_us sysctl setting.
Example A:
On a single CPU machine and there are two cgroups with different CFS periods defined. The quotas of each cgroup represent 50% of CPU time, totalling 100%.
cgroup-A: cpu.cfs_period_us=100ms
cpu.cfs_quota_us=50ms
cgroup-B: cpu.cfs_period_us=1000ms
cpu.cfs_quota_us=500ms
If each cgroup has a single process running, how are these processes scheduled given the CFS period (assuming both processes constantly require CPU time)?
Example B: What happens when cgroup-B have a higher quota than what's actually physically possible to fulfill, ie. cgroup-B set a 90% of the CPU time, and cgroup-A continues to set a quota to be 50% of the CPU time.
cgroup-A: cpu.cfs_period_us=100ms
cpu.cfs_quota_us=50ms
cgroup-B: cpu.cfs_period_us=1000ms
cpu.cfs_quota_us=900ms
How would CFS schedule the processes in this case when the quota is oversubscribed?
Thanks!
linux-kernel cgroups
asked 13 mins ago
Otto YiuOtto Yiu
61
New contributor
Otto Yiu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
I think by typing this question out... I'm starting to gain some clarity. Correct me if I'm wrong here. If cfs_period and quota is merely used for accounting, where the period is a timer which periodically reset the usage in CPU time per cgroup - and where quota is used to compare with actual usage. Then only if the usage exceeds quota during the evaluation period, do the process get throttled and pre-empted. Does that sound sane?
– Otto Yiu
25 secs ago
add a comment |
I've been trying to understand how the Completely Fair Scheduler in the Linux kernel does CPU bandwidth control.
After many readings, I still cannot wrap my head around how the CFS allows for each cgroup to define its own CFS period and how that ties in to the kernel.sched_cfs_bandwidth_slice_us sysctl setting.
Example A:
On a single CPU machine and there are two cgroups with different CFS periods defined. The quotas of each cgroup represent 50% of CPU time, totalling 100%.
cgroup-A: cpu.cfs_period_us=100ms
cpu.cfs_quota_us=50ms
cgroup-B: cpu.cfs_period_us=1000ms
cpu.cfs_quota_us=500ms
If each cgroup has a single process running, how are these processes scheduled given the CFS period (assuming both processes constantly require CPU time)?
Example B: What happens when cgroup-B have a higher quota than what's actually physically possible to fulfill, ie. cgroup-B set a 90% of the CPU time, and cgroup-A continues to set a quota to be 50% of the CPU time.
cgroup-A: cpu.cfs_period_us=100ms
cpu.cfs_quota_us=50ms
cgroup-B: cpu.cfs_period_us=1000ms
cpu.cfs_quota_us=900ms
How would CFS schedule the processes in this case when the quota is oversubscribed?
Thanks!
linux-kernel cgroups
asked 13 mins ago
Otto YiuOtto Yiu
61
New contributor
Otto Yiu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
I've been trying to understand how the Completely Fair Scheduler in the Linux kernel does CPU bandwidth control.
After many readings, I still cannot wrap my head around how the CFS allows for each cgroup to define its own CFS period and how that ties in to the kernel.sched_cfs_bandwidth_slice_us sysctl setting.
Example A:
On a single CPU machine and there are two cgroups with different CFS periods defined. The quotas of each cgroup represent 50% of CPU time, totalling 100%.
cgroup-A: cpu.cfs_period_us=100ms
cpu.cfs_quota_us=50ms
cgroup-B: cpu.cfs_period_us=1000ms
cpu.cfs_quota_us=500ms
If each cgroup has a single process running, how are these processes scheduled given the CFS period (assuming both processes constantly require CPU time)?
Example B: What happens when cgroup-B have a higher quota than what's actually physically possible to fulfill, ie. cgroup-B set a 90% of the CPU time, and cgroup-A continues to set a quota to be 50% of the CPU time.
cgroup-A: cpu.cfs_period_us=100ms
cpu.cfs_quota_us=50ms
cgroup-B: cpu.cfs_period_us=1000ms
cpu.cfs_quota_us=900ms
How would CFS schedule the processes in this case when the quota is oversubscribed?
Thanks!
linux-kernel cgroups
linux-kernel cgroups
asked 13 mins ago
Otto YiuOtto Yiu
61
New contributor
Otto Yiu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 13 mins ago
Otto YiuOtto Yiu
61
New contributor
Otto Yiu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 13 mins ago
Otto YiuOtto Yiu
61
New contributor
Otto Yiu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 13 mins ago
Otto YiuOtto Yiu
61
asked 13 mins ago
Otto YiuOtto Yiu
61
61
New contributor
Otto Yiu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Otto Yiu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Otto Yiu is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
I think by typing this question out... I'm starting to gain some clarity. Correct me if I'm wrong here. If cfs_period and quota is merely used for accounting, where the period is a timer which periodically reset the usage in CPU time per cgroup - and where quota is used to compare with actual usage. Then only if the usage exceeds quota during the evaluation period, do the process get throttled and pre-empted. Does that sound sane?
– Otto Yiu
25 secs ago
add a comment |
I think by typing this question out... I'm starting to gain some clarity. Correct me if I'm wrong here. If cfs_period and quota is merely used for accounting, where the period is a timer which periodically reset the usage in CPU time per cgroup - and where quota is used to compare with actual usage. Then only if the usage exceeds quota during the evaluation period, do the process get throttled and pre-empted. Does that sound sane?
– Otto Yiu
25 secs ago
I think by typing this question out... I'm starting to gain some clarity. Correct me if I'm wrong here. If cfs_period and quota is merely used for accounting, where the period is a timer which periodically reset the usage in CPU time per cgroup - and where quota is used to compare with actual usage. Then only if the usage exceeds quota during the evaluation period, do the process get throttled and pre-empted. Does that sound sane?
– Otto Yiu
25 secs ago
I think by typing this question out... I'm starting to gain some clarity. Correct me if I'm wrong here. If cfs_period and quota is merely used for accounting, where the period is a timer which periodically reset the usage in CPU time per cgroup - and where quota is used to compare with actual usage. Then only if the usage exceeds quota during the evaluation period, do the process get throttled and pre-empted. Does that sound sane?
– Otto Yiu
25 secs ago
add a comment |
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I think by typing this question out... I'm starting to gain some clarity. Correct me if I'm wrong here. If cfs_period and quota is merely used for accounting, where the period is a timer which periodically reset the usage in CPU time per cgroup - and where quota is used to compare with actual usage. Then only if the usage exceeds quota during the evaluation period, do the process get throttled and pre-empted. Does that sound sane?
– Otto Yiu
25 secs ago