Messages in this thread | | | From | Paul Turner <> | Date | Sat, 26 Nov 2011 05:07:12 -0800 | Subject | Re: [PATCH v2 14/14] Change CPUACCT to default n |
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On Thu, Nov 24, 2011 at 6:05 PM, Li Zefan <lizf@cn.fujitsu.com> wrote: >> despite it being a not entirely natural fit. Something I proposed at >> Prague and that we could explore here is the idea of a co-mounted >> controller. In this example it would only be mountable with cpu so >> you could always depend on the cpu hierarchy being there; likewise we >> can put (jump-labeled) touchpoints within the cpu-subsystem to call >> out for updates as appropriate when the co-mount exists. >> > > IIUC, this co-mounting idea is something I implemented years ago: > > https://lkml.org/lkml/2008/6/18/389 > > The use case and the reason it was rejected: > > https://lkml.org/lkml/2008/7/1/97 >
Rejection is a bit of a strong statement -- the idea seemed amenable but lacking a strong use-case. That said, taking a deep look at some of what Glauber is trying to do in this series I don't think it's something that would help here.
For this discussion the motivation for a co-mount would be to piggy-back on the cpu sub-systems own hierarchy walks to reduce overhead. However, this is not structured in a way that can take advantage of this, and, looking at what Glauber is attempting to collect it's not clear that it can be.
I think this moves the discussion towards whether we should consider deprecating some of the exported fields (namely usage and usage_per_cpu) from cpuacct instead of the entire controller as we had initially desired. This would allow cpuacct to exist with a much lower overhead, especially within the context-switch path.
- Paul
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