Messages in this thread | | | Date | Mon, 15 Dec 2008 13:58:18 +0100 | From | "stephane eranian" <> | Subject | Re: [patch] Performance Counters for Linux, v3 |
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Hi,
On Mon, Dec 15, 2008 at 1:37 AM, Paul Mackerras <paulus@samba.org> wrote: > Ingo Molnar writes: > >> * 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? >> Could you explain what you mean by sharing here?
Are you talking about time multiplexing the counter?
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