Messages in this thread |  | | Date | Fri, 21 May 2010 11:40:53 +0200 | | From | Ingo Molnar <> | | Subject | [rfc] Describe events in a structured way via sysfs |
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* Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, 2010-05-20 at 16:12 -0700, Greg KH wrote:
> > How deep in the device tree are you really going to be > > caring about? It sounds like the large majority of > > events are only going to be coming from the "system" > > type objects (cpu, nodes, memory, etc.) and very few > > would be from things that we consider a 'struct > > device' today (like a pci, usb, scsi, or input, etc.) > > The general noise I hear from the hardware people is > that we'll see more and more device-level stuff - bus > bridges/controller and actual devices (GPUs, NICs etc.) > will be wanting to export performance metrics.
There's (much) more:
- laptops want to provide power level/usage metrics,
- we could express a lot of special, lower level (transport specific) disk IO stats via events as well - without having to push those stats to a higher level (where it might not make sense). Currently such kinds of stats/metrics are very device/subsystem specific way, if they are provided at all.
Also, we already have quite a few per device tracepoints upstream. Here are a few examples:
- GPU tracepoints (trace_i915_gem_request_submit(), etc.) - WIFI tracepoints (trace_iwlwifi_dev_ioread32(), etc.) - block tracepoints (trace_block_bio_complete())
So these would be attached to:
# GEM events of drm/card0: /sys/devices/pci0000:00/0000:00:02.0/drm/card0/events/i915_gem_request_submit/
# Wifi-ioread events of wlan0: /sys/devices/pci0000:00/0000:00:1c.1/0000:03:00.0/net/wlan0/events/iwlwifi_dev_ioread32/
# whole sdb disk events: /sys/block/sdb/events/block_bio_complete/
# sdb1 partition events: /sys/block/sdb/sdb1/events/block_bio_complete/
And we also have 'software nodes' in /sys that have events upstream here and today. For example for SLAB we already have kmalloc/kfree tracepoints (trace_kmalloc() and trace_kfree()):
# all kmalloc events: /sys/kernel/slab/events/
# kmalloc events for sighand_cache: /sys/kernel/slab/sighand_cache/events/kmalloc/
# kfree events for sighand_cache: /sys/kernel/slab/sighand_cache/events/kfree/
In general the set of events we have upstream is growing along an exponential curve (there's over a hundred now, via tracepoints).
They are either logically attached to the hardware topology of the system (as in the first set of examples above), or ae attached to the software/subsystem object topology of the kernel (some examples of which are described in the second set of examples above).
Sometimes there are aliasing/filtering relationship between events, which is expressed very well via the hierarchy and granularity of /sysfs.
New events would go into that topology there in a natural way.
For example general hugepage tracepoints (should we introduce any) would go into the existing hugepage node:
/sys/kernel/mm/hugepages/events/...
All in one, all these existing and future events, both of hardware and software type, are literally begging to be attached to nodes in /sys :-)
If we created a separate eventfs for it we'd have to start with duplicating all the topology/hiearchy/structure that is present in sysfs already. (and dilluting /sys's utility)
That would be a bad thing, so it would be nice if we found a workable solution here. We could split up the record format some more:
/sys/kernel/sched/events/sched_wakeup/format/ /sys/kernel/sched/events/sched_wakeup/format/common_type/ /sys/kernel/sched/events/sched_wakeup/format/common_flags/ /sys/kernel/sched/events/sched_wakeup/format/common_preempt_count/ /sys/kernel/sched/events/sched_wakeup/format/common_pid/ /sys/kernel/sched/events/sched_wakeup/format/common_lock_depth/ /sys/kernel/sched/events/sched_wakeup/format/comm/ /sys/kernel/sched/events/sched_wakeup/format/pid/ /sys/kernel/sched/events/sched_wakeup/format/prio/ /sys/kernel/sched/events/sched_wakeup/format/success/ /sys/kernel/sched/events/sched_wakeup/format/target_cpu/
Into single-value files. But this would add significant parsing overhead (plus significant allocation overhead), for no tangible benefit.
The problem with /proc was always the lack of standard structure and the lack of performance - while the format file is about _more_ structure.
Increasing structure parsing overhead does not look like the right answer to that problem.
Hm?
Ingo
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