* [PATCH] [RFT] drm/i915: Don't waste our paultry cache on a context object
@ 2013-09-20 15:05 Ben Widawsky
2013-09-20 15:12 ` Chris Wilson
0 siblings, 1 reply; 3+ messages in thread
From: Ben Widawsky @ 2013-09-20 15:05 UTC (permalink / raw)
To: Intel GFX; +Cc: Eero Tamminen, Ben Widawsky, Ben Widawsky
Context save and restore is by definition a slow process, however it is
also an infrequent process. Don't try to optimize the save restore at
the cost of any of our precious cache space. Contexts begin to get quite
large on HSW and beyond.
At least for benchmarks people seem to care about, there is almost
always only 1 context running, which means I don't expect this to do any
harm. For benchmarks with many contexts, there could be performance
degradation - but I have a sneaking suspicion the HW will do some fancy
magic to speak up context save & restores anyway.
CC: Chris Wilson <chris@chris-wilson.co.uk>
CC: Eero Tamminen <eero.t.tamminen@intel.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
---
drivers/gpu/drm/i915/i915_gem_context.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 26c3fcc..593be55 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -153,13 +153,10 @@ create_hw_context(struct drm_device *dev,
return ERR_PTR(-ENOMEM);
}
- if (INTEL_INFO(dev)->gen >= 7) {
- ret = i915_gem_object_set_cache_level(ctx->obj,
- I915_CACHE_L3_LLC);
- /* Failure shouldn't ever happen this early */
- if (WARN_ON(ret))
- goto err_out;
- }
+ ret = i915_gem_object_set_cache_level(ctx->obj, I915_CACHE_NONE);
+ /* Failure shouldn't ever happen this early */
+ if (WARN_ON(ret))
+ goto err_out;
/* The ring associated with the context object is handled by the normal
* object tracking code. We give an initial ring value simple to pass an
--
1.8.4
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH] [RFT] drm/i915: Don't waste our paultry cache on a context object
2013-09-20 15:05 [PATCH] [RFT] drm/i915: Don't waste our paultry cache on a context object Ben Widawsky
@ 2013-09-20 15:12 ` Chris Wilson
2013-09-20 15:24 ` Ben Widawsky
0 siblings, 1 reply; 3+ messages in thread
From: Chris Wilson @ 2013-09-20 15:12 UTC (permalink / raw)
To: Ben Widawsky; +Cc: Intel GFX, Eero Tamminen, Ben Widawsky
On Fri, Sep 20, 2013 at 08:05:02AM -0700, Ben Widawsky wrote:
> Context save and restore is by definition a slow process, however it is
> also an infrequent process. Don't try to optimize the save restore at
> the cost of any of our precious cache space. Contexts begin to get quite
> large on HSW and beyond.
Infrequent?
> At least for benchmarks people seem to care about, there is almost
> always only 1 context running, which means I don't expect this to do any
> harm. For benchmarks with many contexts, there could be performance
> degradation - but I have a sneaking suspicion the HW will do some fancy
> magic to speak up context save & restores anyway.
There are at least 2 contexts in every benchmark QA cares about. It
wasn't like making them L3 objects in the first place was motivated by
benchmark results...
Anyway the idea was to see if QA still notice a difference...
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] [RFT] drm/i915: Don't waste our paultry cache on a context object
2013-09-20 15:12 ` Chris Wilson
@ 2013-09-20 15:24 ` Ben Widawsky
0 siblings, 0 replies; 3+ messages in thread
From: Ben Widawsky @ 2013-09-20 15:24 UTC (permalink / raw)
To: Chris Wilson, Ben Widawsky, Intel GFX, Eero Tamminen
On Fri, Sep 20, 2013 at 04:12:37PM +0100, Chris Wilson wrote:
> On Fri, Sep 20, 2013 at 08:05:02AM -0700, Ben Widawsky wrote:
> > Context save and restore is by definition a slow process, however it is
> > also an infrequent process. Don't try to optimize the save restore at
> > the cost of any of our precious cache space. Contexts begin to get quite
> > large on HSW and beyond.
>
> Infrequent?
Relative to operations which use the cache.
>
> > At least for benchmarks people seem to care about, there is almost
> > always only 1 context running, which means I don't expect this to do any
> > harm. For benchmarks with many contexts, there could be performance
> > degradation - but I have a sneaking suspicion the HW will do some fancy
> > magic to speak up context save & restores anyway.
>
> There are at least 2 contexts in every benchmark QA cares about. It
> wasn't like making them L3 objects in the first place was motivated by
> benchmark results...
>
No, I've no doubt it was motivated by benchmarks, but I think making it
L3 (which I still have a hard time believe would do at all what it's
intended to do) would only prove further that not wasting LLC space is a
good thing. The theory follows that not wasting L3 space is also a good
thing.
> Anyway the idea was to see if QA still notice a difference...
> -Chris
>
I'll try to be an optimist for once.
--
Ben Widawsky, Intel Open Source Technology Center
^ permalink raw reply [flat|nested] 3+ messages in thread
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2013-09-20 15:05 [PATCH] [RFT] drm/i915: Don't waste our paultry cache on a context object Ben Widawsky
2013-09-20 15:12 ` Chris Wilson
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