Re: [Xen-devel] [PATCH 06/15] xen: trace IRQ enabling/disabling

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 01/06/17 18:34, Dario Faggioli wrote:
> Trace when interrupts are disabled and (re)enabled.
> Basically, we replace the IRQ disabling and enabling
> functions with helpers that does the same, but also
> output the proper trace record.
> 
> For putting in the record something that will let
> us identify _where_ in the code (i.e., in what function)
> the IRQ manipulation is happening, use either:
>  - current_text_addr(),
>  - or __builtin_return_address(0).
> 
> In fact, depending on whether the disabling/enabling
> happens in macros (like for local_irq_disable() and
> local_irq_enable()) or in actual functions (like in
> spin_lock_irq*()), it is either:
>  - the actual content of the instruction pointer when
>    IRQ are disabled/enabled,
>  - or the return address of the utility function where
>    IRQ are disabled/enabled,
> that will tell us what it is the actual piece of code
> that is asking for the IRQ manipulation operation.
> 
> Gate this with its specific Kconfig option, and keep
> it in disabled state by default (i.e., don't build it,
> if not explicitly specified), as the impact on
> performance may be non negligible.
> 
> Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
> ---
> Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Cc: Jennifer Herbert <jennifer.herbert@xxxxxxxxxx>
> ---
>  xen/Kconfig.debug                  |   11 ++++-
>  xen/common/spinlock.c              |   16 +++++--
>  xen/common/trace.c                 |   10 +++-
>  xen/include/asm-arm/arm32/system.h |   12 +++++
>  xen/include/asm-arm/arm64/system.h |   12 +++++
>  xen/include/asm-x86/system.h       |   85 
> ++++++++++++++++++++++++++++++++++--
>  xen/include/public/trace.h         |    2 +
>  xen/include/xen/rwlock.h           |   33 +++++++++++---
>  8 files changed, 161 insertions(+), 20 deletions(-)
> 
> diff --git a/xen/Kconfig.debug b/xen/Kconfig.debug
> index 374c1c0..81910c9 100644
> --- a/xen/Kconfig.debug
> +++ b/xen/Kconfig.debug
> @@ -98,7 +98,7 @@ config PERF_ARRAYS
>       ---help---
>         Enables software performance counter array histograms.
>  
> -config TRACING
> +menuconfig TRACING
>       bool "Tracing"
>       default y
>       ---help---
> @@ -106,6 +106,15 @@ config TRACING
>         in per-CPU ring buffers. The 'xentrace' tool can be used to read
>         the buffers and dump the content on the disk.
>  
> +config TRACE_IRQSOFF
> +     bool "Trace when IRQs are disabled and (re)enabled" if EXPERT = "y"
> +     default n
> +     depends on TRACING
> +     ---help---
> +       Makes it possible to generate events _every_ time IRQs are disabled
> +          and (re)enabled, with also an indication of where that happened.
> +          Note that this comes with high overead and produces huge amount of
> +          tracing data.

*overhead (yours is missing an 'h')

I think I might emphasize that the overhead well be present even when
tracing is off.  What about something like this?

"Note that this comes with an overhead even when tracing is disabled;
and has a high overhead and produces a large amount of tracing data when
enabled."

With that change:

Acked-by: George Dunlap <george.dunlap@xxxxxxxxxx>


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