[1/2] UBUNTU: [Config] enable MMIOTRACE for graphics debugging

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.

Signed-off-by: Andy Whitcroft <apw@canonical.com>
---
 debian.master/config/config.common.ubuntu |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

It seems at least worth trying as everything that helps to debug is good as long
as it does not impact normal usage.

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.
> 
> Signed-off-by: Andy Whitcroft <apw@canonical.com>
Acked-by: Stefan Bader <stefan.bader@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

The benefit as a debugging tool makes this a very good option to turn
on. It appears to add minimal overhead when not being used in debug
mode, so I'm for this. 

On Wed, 2010-03-17 at 09:26 +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.
> 
> Signed-off-by: Andy Whitcroft <apw@canonical.com>
Acked-by: Colin King <colin.king@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
> 
>

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

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

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.

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