Messages in this thread | | | From | Andy Lutomirski <> | Date | Fri, 3 Oct 2014 14:56:56 -0700 | Subject | Re: [tip:x86/asm] x86: Speed up ___preempt_schedule*() by using THUNK helpers |
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On Fri, Oct 3, 2014 at 2:41 PM, Oleg Nesterov <oleg@redhat.com> wrote: > On 10/03, Chuck Ebbert wrote: >> >> > [ 921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44) >> > [ 921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145) >> > [ 921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44) >> > [ 921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145) >> > [ 921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44) >> > [ 921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145) >> > [ 921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44) >> > [ 921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145) >> > [ 921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44) >> > [ 921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145) >> >> <snip lots of repeats of this> >> >> I *think* this is because RBP isn't being saved across task switch >> anymore? >> >> Without CONFIG_FRAME_POINTERS that night not be a problem... > > Could you please spell? > > I don't even understand "RBP isn't being saved", SAVE_CONTEXT/RESTORE_CONTEXT > do push/pop %rbp? >
Is this thing missing a flags or cc clobber:
# define __preempt_schedule() asm ("call ___preempt_schedule")
Also, I'm at a loss as to wtf all this code is doing.
There's preempt_schedule, which appears to be a normal C function.
There's ___preempt_schedule, which is written in assembly and calls preempt_schedule.
Then there's __preempt_schedule, which is an inline assembler function that calls ___preempt_schedule.
Is this all just to make the call sequence for preempt_schedule shorter?
--Andy
> Thanks, > > Oleg. >
-- Andy Lutomirski AMA Capital Management, LLC
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