Messages in this thread | | | Date | Wed, 25 Mar 2015 18:29:22 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 2/4] x86/asm/entry/64: do not TRACE_IRQS fast SYSRET64 path |
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* Denys Vlasenko <dvlasenk@redhat.com> wrote:
> SYSRET code path has a small irq-off block. > On this code path, TRACE_IRQS_ON can't be called right before interrupts > are enabled for real, we can't clobber registers there. > So current code does it earlier, in a safe place. > > But with this, TRACE_IRQS_OFF/ON frames just two fast instructions, > which is ridiculous: now most of irq-off block is _outside_ of the framing. > > Do the same thing that we do on SYSCALL entry: do not track this irq-off block, > it is very small to ever cause noticeable irq latency. > > Be careful: make sure that "jnz int_ret_from_sys_call_irqs_off" now does > invoke TRACE_IRQS_OFF - move int_ret_from_sys_call_irqs_off label before > TRACE_IRQS_OFF.
> @@ -345,8 +346,8 @@ tracesys_phase2: > */ > GLOBAL(int_ret_from_sys_call) > DISABLE_INTERRUPTS(CLBR_NONE) > - TRACE_IRQS_OFF > int_ret_from_sys_call_irqs_off: > + TRACE_IRQS_OFF > movl $_TIF_ALLWORK_MASK,%edi > /* edi: mask to check */
This latter trick absolutely needs a comment, to keep future lockdep developers from wondering about the mismatch and the weird label placement ...
Thanks,
Ingo
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