Messages in this thread | | | Date | Fri, 2 Jan 2015 09:02:23 -0800 | From | Shaohua Li <> | Subject | Re: [PATCH v2 3/3] X86: Add a thread cpu time implementation to vDSO |
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On Fri, Jan 02, 2015 at 08:31:33AM -0700, David Ahern wrote: > On 1/1/15 7:59 PM, Shaohua Li wrote: > >I'm wondering how we could use the perf to implament a clock_gettime. > >reading the perf fd or using ioctl is slow so reading the mmap > >ringbuffer is the only option. But as far as I know the ringbuffer has > >data only when an event is generated. Between two events, there is > >nothing we can read from the ringbuffer. Then how can application get > >time info in the interval? > > Are you wanting to read perf_clock from userspace?
Yep, in some sort of form. Basically I want to read the time a task runs. Peter suggests we can read the activation time of a perf event. But I don't want to use any system call, as it's slow and likes clock_gettime.
Thanks, Shaohua
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