Messages in this thread | | | Subject | Re: [PATCH] update fix X86_64 procfs provide stack information for threads | From | Stefani Seibold <> | Date | Wed, 04 Nov 2009 13:22:49 +0100 |
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Am Mittwoch, den 04.11.2009, 13:00 +0100 schrieb Andi Kleen: > > This is true, but i think it is better to get an outdated value than a > > complete wrong value like -1. > > -1 means "I don't know". I don't think "completely wrong" > is the correct term to describe that. > > > The truth is that KSTK_ESP always return an outdated value on a multi > > core system if the process never do a system call. > > I think not supporting updates on interrupts at least is very poor. > Unfortunately there's no good way fast path way to detect this I know of > (that is why I originally added -1 here) >
I am sorry, i did not know that was your code. But anyway.
> > > Question: is task_pt_regs(task)->sp set in 64 bit mode when the process > > is blocked in an interrupt? If true, we can add two additional assembly > > instruction to the system call handler and store the stack pointer into > > this. Than KSTK_ESP wil be again a simple macro like > > You want to add instructions to one of the hottest kernel paths > for this hyper-obscure application? Bad idea. >
You complain that the the value is outdated and i told you how you can get a more accuracy value. I agree that this is bad idea.
> My recommendation would be to just deprecate this proc field > and if anyone really wants that information they can use > a trivial ptrace() based user program. >
I spend a lot of time doing this, it would be nice to give it a change a fix the KSTK_ESP macro. It will be not only used by my code. It would be great if we can do this together.
You have the knowledge, so i will ask my question again: Is task_pt_regs(task)->sp set in 64 bit mode when the process is block in an interrupt? Is there a way to detected if a process is blocked by an interrupt?
If you answer both with true than i can fix KSTK_ESP without performance penalty for the rest of the system.
Stefani
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