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SubjectRe: [PATCH 3/3] context_tracking,x86: remove extraneous irq disable & enable from context tracking on syscall entry
On 05/07/2015 08:29 AM, Ingo Molnar wrote:
> * Frederic Weisbecker <> wrote:
>>>> We cannot take the lock_trace(task) from irq context, and we
>>>> probably do not need to anyway, since we do not care about a
>>>> precise stack trace for the task.
>>> So one worry with this and similar approaches of statistically
>>> detecting user mode would be the fact that on the way out to
>>> user-space we don't really destroy the previous call trace - we
>>> just pop off the stack (non-destructively), restore RIPs and are
>>> gone.
>>> We'll need that percpu flag I suspect.
>> Note we have the context tracking state which tells where the
>> current task is: user/system/guest.
> Yes, but that overhead is what I'm suggesting we get rid of, I thought
> Rik was trying to find a mechanism that would be independent of that?

One thing at a time :)

I am working on the timer sampling stuff, which should be easy
to adapt to a different user/system/guest/irq/softirq/... tracking
thing, if somebody else comes up with a more efficient way to do

All rights reversed

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