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Old 03-17-2010, 09:03 AM
Bryce Harrington
 
Default enable MMIOTRACE for graphics debugging

On Wed, Mar 17, 2010 at 09:26:24AM +0000, Andy Whitcroft wrote:
> Enable MMIOTRACE to allow us to trace low level card operations. This is
> commonly used to debug graphics issues particularly under Nouveau.
> According to the documentation it is a near zero impact when disabled.

"when enabled" I hope?

> Signed-off-by: Andy Whitcroft <apw@canonical.com>
> ---
> debian.master/config/config.common.ubuntu | 3 ++-
> 1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/debian.master/config/config.common.ubuntu b/debian.master/config/config.common.ubuntu
> index 0bca70a..989c14c 100644
> --- a/debian.master/config/config.common.ubuntu
> +++ b/debian.master/config/config.common.ubuntu
> @@ -2236,7 +2236,8 @@ CONFIG_MMC_TIFM_SD=m
> # CONFIG_MMC_UNSAFE_RESUME is not set
> CONFIG_MMC_VIA_SDMMC=m
> CONFIG_MMC_WBSD=m
> -# CONFIG_MMIOTRACE is not set
> +CONFIG_MMIOTRACE=y
> +# CONFIG_MMIOTRACE_TEST is not set
> CONFIG_MMU=y
> CONFIG_MMU_NOTIFIER=y
> CONFIG_MM_OWNER=y
> --
> 1.7.0
>
>
> --
> kernel-team mailing list
> kernel-team@lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team

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Old 03-17-2010, 09:20 AM
Andy Whitcroft
 
Default enable MMIOTRACE for graphics debugging

On Wed, Mar 17, 2010 at 03:03:41AM -0700, Bryce Harrington wrote:
> On Wed, Mar 17, 2010 at 09:26:24AM +0000, Andy Whitcroft wrote:
> > Enable MMIOTRACE to allow us to trace low level card operations. This is
> > commonly used to debug graphics issues particularly under Nouveau.
> > According to the documentation it is a near zero impact when disabled.
>
> "when enabled" I hope?

The cost is near-zero for having the MMIOTRACE option enabled with the
trace collection turned off (the default). We take one additional branch
in the mmio map/upmap paths which are non-critical initialisation/teardone
paths in normal usage. The actual mmio operations are not affected at all.
When we enable trace collection the overhead is high, taking a page
fault for each access to the mmio mapping.

-apw

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Old 03-18-2010, 04:43 AM
Christopher James Halse Rogers
 
Default enable MMIOTRACE for graphics debugging

On Wed, 2010-03-17 at 03:03 -0700, Bryce Harrington wrote:
> On Wed, Mar 17, 2010 at 09:26:24AM +0000, Andy Whitcroft wrote:
> > Enable MMIOTRACE to allow us to trace low level card operations. This is
> > commonly used to debug graphics issues particularly under Nouveau.
> > According to the documentation it is a near zero impact when disabled.
>
> "when enabled" I hope?
>
No; when it's enabled it's a huge performance hit. It's not uncommon
for a mmio-traced nvidia blob to take multiple minutes to bring up X.
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Old 03-18-2010, 03:50 PM
Scott James Remnant
 
Default enable MMIOTRACE for graphics debugging

On Thu, 2010-03-18 at 16:43 +1100, Christopher James Halse Rogers wrote:

> On Wed, 2010-03-17 at 03:03 -0700, Bryce Harrington wrote:
> > On Wed, Mar 17, 2010 at 09:26:24AM +0000, Andy Whitcroft wrote:
> > > Enable MMIOTRACE to allow us to trace low level card operations. This is
> > > commonly used to debug graphics issues particularly under Nouveau.
> > > According to the documentation it is a near zero impact when disabled.
> >
> > "when enabled" I hope?
> >
> No; when it's enabled it's a huge performance hit. It's not uncommon
> for a mmio-traced nvidia blob to take multiple minutes to bring up X.
>
To be clear here:

The kernel config option, when enabled, adds a new available tracer,
which when itself is enabled, causes a huge performance hit.

Enabling the kernel config option doesn't cause a huge performance hit
in its own right.

Scott
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