Messages in this thread | | | From | Venkatesh Pallipadi <> | Subject | [PATCH 0/4] Finer granularity and task/cgroup irq time accounting | Date | Mon, 19 Jul 2010 16:57:11 -0700 |
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Earlier version of this patchset here - lkml subject: "[RFC PATCH 0/4] Finer granularity and task/cgroup irq time accounting" http://marc.info/?l=linux-kernel&m=127474630527689&w=2
Currently, the softirq and hardirq time reporting is only done at the CPU level. There are usecases where reporting this time against task or task groups or cgroups will be useful for user/administrator in terms of resource planning and utilization charging. Also, as the accoounting is already done at the CPU level, reporting the same at the task level does not add any significant computational overhead other than task level storage (patch 1).
The softirq/hardirq statistics commonly done based on tick based sampling. Though some archs have CONFIG_VIRT_CPU_ACCOUNTING based fine granularity accounting. Having similar mechanism to get fine granularity accounting on x86 will be a major challenge, given the state of TSC reliability on various platforms and also the overhead it may add in common paths like syscall entry exit.
An alternative is to have a generic (sched_clock based) and configurable fine-granularity accounting of si and hi time which can be reported over the /proc/<pid>/stat API (patch 2).
Patch 3 and 4 are exporting this info at the cgroup level.
Changes since the original RFC - * General code cleanup and documentation for new APIs added. * Handle notsc option by having a runtime flag sched_clock_irqtime, along with the original CONFIG_IRQ_TIME_ACCOUNTING option. Peter Zijlstra suggested the use of alternate instruction kind of mechanism here. But, that is mostly x86 specific and not generic. The irq time accounting code is mostly generic. * Did performance runs with various systems with tsc based sched_clock - both with and without sched_clock_stable - running tbench, dbench, SPECjbb and did not notice any measurable slowness when this option is enabled. Todo - * Peter Zijlstra suggested modifying scale_rt_power to account for irq time. I have a patch for that and have been testing that right now. But, that change is not very pretty as yet and also will need some more testing. Feels better to make that a separate change. Will follow up on that soon.
Thanks, Venki
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