Re: [PATCH 15/17] drm/i915: Increase GuC log buffer size to reduce flush interrupts

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 10/07/16 14:41, akash.goel@intel.com wrote:
> From: Akash Goel <akash.goel@intel.com>
>
> In cases where GuC generate logs at a very high rate, correspondingly
> the rate of flush interrupts is also very high.
> So far total 8 pages were allocated for storing both ISR & DPC logs.
> As per the half-full draining protocol followed by GuC, by doubling
> the number of pages, the frequency of flush interrupts can be cut down
> to almost half, which then helps in reducing the logging overhead.
> So now allocating 8 pages apiece for ISR & DPC logs.
>
> Suggested-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Signed-off-by: Akash Goel <akash.goel@intel.com>
> ---
>   drivers/gpu/drm/i915/intel_guc_fwif.h | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_guc_fwif.h b/drivers/gpu/drm/i915/intel_guc_fwif.h
> index 1de6928..7521ed5 100644
> --- a/drivers/gpu/drm/i915/intel_guc_fwif.h
> +++ b/drivers/gpu/drm/i915/intel_guc_fwif.h
> @@ -104,9 +104,9 @@
>   #define   GUC_LOG_ALLOC_IN_MEGABYTE	(1 << 3)
>   #define   GUC_LOG_CRASH_PAGES		1
>   #define   GUC_LOG_CRASH_SHIFT		4
> -#define   GUC_LOG_DPC_PAGES		3
> +#define   GUC_LOG_DPC_PAGES		7
>   #define   GUC_LOG_DPC_SHIFT		6
> -#define   GUC_LOG_ISR_PAGES		3
> +#define   GUC_LOG_ISR_PAGES		7
>   #define   GUC_LOG_ISR_SHIFT		9
>   #define   GUC_LOG_BUF_ADDR_SHIFT	12
>
> @@ -436,9 +436,9 @@ enum guc_log_buffer_type {
>    *        |   Crash dump state header     |
>    * Page1  +-------------------------------+
>    *        |           ISR logs            |
> - * Page5  +-------------------------------+
> - *        |           DPC logs            |
>    * Page9  +-------------------------------+
> + *        |           DPC logs            |
> + * Page17 +-------------------------------+
>    *        |         Crash Dump logs       |
>    *        +-------------------------------+
>    *
>

I don't mind - but does it help? And how much and for what? Haven't you 
later found that the uncached reads were the main issue?

Regards,

Tvrtko
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