Messages in this thread | | | Date | Mon, 15 Dec 2008 00:13:32 +0100 | From | Ingo Molnar <> | Subject | Re: [patch] Performance Counters for Linux, v3 |
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* stephane eranian <eranian@googlemail.com> wrote:
> Hi, > > Given the level of abstractions you are using for the API, and given > your argument that the kernel can do the HW resource scheduling better > than anybody else. > > What happens in the following test case: > > - 2-way system (cpu0, cpu1) > > - on cpu0, two processes P1, P2, each self-monitoring and counting event E1. > Event E1 can only be measured on counter C1. > > - on cpu1, there is a cpu-wide session, monitoring event E1, thus using C1 > > - the scheduler decides to migrate P1 onto CPU1. You now have a > conflict on C1. > > How is this managed?
If there's a single unit of sharable resource [such as an event counter, or a physical CPU], then there's just three main possibilities: either user 1 gets it all, or user 2 gets it all, or they share it.
We've implemented the essence of these variants, with sharing the resource being the sane default, and with the sysadmin also having a configuration vector to reserve the resource to himself permanently. (There could be more variations of this.)
What is your point?
Ingo
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