Messages in this thread |  | | | Subject | Re: [PATCH 2/2] perf: Use hot regs with software sched switch/migrate events | | From | Peter Zijlstra <> | | Date | Mon, 29 Mar 2010 10:49:59 +0200 |
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On Sun, 2010-03-28 at 07:11 +0200, Frederic Weisbecker wrote: > Scheduler's task migration events don't work because they always > pass NULL regs perf_sw_event(). The event hence gets filtered > in perf_swevent_add(). > > Scheduler's context switches events use task_pt_regs() to get > the context when the event occured which is a wrong thing to > do as this won't give us the place in the kernel where we went > to sleep but the place where we left userspace. The result is > even more wrong if we switch from a kernel thread. > > Use the hot regs snapshot for both events as they belong to the > non-interrupt/exception based events family. Unlike page faults > or so that provide the regs matching the exact origin of the event, > we need to save the current context. > > This makes the task migration event working and fix the context > switch callchains and origin ip.
But after this its no longer possible to profile userspace on context switches is it?
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