Re: [PATCH] remove LOCK_SECTION from x86_64 spin_lock asm
From: Andi Kleen (ak_at_suse.de)
Date: 09/16/04
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Date: Thu, 16 Sep 2004 09:53:39 +0200 To: Ingo Molnar <mingo@elte.hu>
On Thu, Sep 16, 2004 at 09:44:31AM +0200, Ingo Molnar wrote:
> it only works on pointer less kernels because the spinlock profile
> unwinding is _conditional_ on an FP kernel right now:
>
> #if defined(CONFIG_SMP) && defined(CONFIG_FRAME_POINTER)
> unsigned long profile_pc(struct pt_regs *regs)
> {
> ...
>
> on non-FP kernels you'll see all the overhead in the single spin_lock()
> function, agreed?
Agreed. Ok, should be easy to fix with the same scheme, except
that it has to use offset 0 instead of 1 for the !FP case.
I will cook up a patch.
BTW the SMP check is also wrong because preemptive kernels also
need this unwinding, although they should not spend too much
time in locking.
> > > in this respect - it might work if you can detect for sure at build time
> > > whether there's any local variable. Tricks like this really tend to
> > > haunt us later.
> >
> > There are already lots of such assumptions in the kernel (e.g. WCHAN
> > and others). I don't think adding one more is a big issue.
>
> wchan has only one assumption: that that all __sched section functions
It's more than WCHAN, e.g. sysrq-t assumes it too.
-Andi
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- Previous message: Ingo Molnar: "Re: [PATCH] remove LOCK_SECTION from x86_64 spin_lock asm"
- In reply to: Ingo Molnar: "Re: [PATCH] remove LOCK_SECTION from x86_64 spin_lock asm"
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