On 08/03/2018 18:46, Daniele Ceraolo Spurio wrote:
On 08/03/18 01:31, Tvrtko Ursulin wrote:
On 07/03/2018 19:45, Daniele Ceraolo Spurio wrote:
The mmio bases we're currently storing in the intel_engines array are
only valid for a subset of gens, so we need to ignore them and use
different values in some cases. Instead of doing that, we can have a
table of [starting gen, mmio base] pairs for each engine in
intel_engines and select the correct one based on the gen we're running
on in a consistent way.
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
---
drivers/gpu/drm/i915/intel_engine_cs.c | 77
+++++++++++++++++++++------------
drivers/gpu/drm/i915/intel_ringbuffer.c | 1 -
2 files changed, 49 insertions(+), 29 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c
b/drivers/gpu/drm/i915/intel_engine_cs.c
index 4ba139c27fba..1dd92cac8d67 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -81,12 +81,16 @@ static const struct engine_class_info
intel_engine_classes[] = {
},
};
+#define MAX_MMIO_BASES 3
struct engine_info {
unsigned int hw_id;
unsigned int uabi_id;
u8 class;
u8 instance;
- u32 mmio_base;
+ struct engine_mmio_base {
+ u32 gen : 8;
+ u32 base : 24;
+ } mmio_bases[MAX_MMIO_BASES];
unsigned irq_shift;
};
It's not bad, but I am just wondering if it is too complicated versus
simply duplicating the tables.
Duplicated tables would certainly be much less code and complexity,
but what about the size of pure data?
In this patch sizeof(struct engine_info) grows by MAX_MMIO_BASES *
sizeof(u32), so 12, to the total of 30 if I am not mistaken. Times
NUM_ENGINES equals 240 bytes for intel_engines[] array with this scheme.
we remove a u32 (the old mmio base) so we only grow 8 per engine, but
the compiler rounds up to a multiple of u32 so 28 per engine, for a
total of 224.
Separate tables per gens would be:
sizeof(struct engine_info) is 18 bytes.
For < gen6 we'd need 3 engines * 18 = 54
< gen11 = 5 engines * 18 = 90
>= gen11 = 8 engines * 18 = 144
54 + 90 + 144 = 288 bytes
So a little bit bigger. Hm. Plus we would need to refactor so
intel_engines[] is not indexed by engine->id but is contiguous array
with engine->id in the elements. Code to lookup the compact array
should be simpler than combined new code from this patch, especially
if you add the test as Chris suggested. So separate engine info arrays
would win I think overall - when considering size of text + size of
data + size of source code.
Not sure. I would exclude the selftest, which is usually not compiled
for released kernels, which leads to:
Yes, but we cannot exclude its source since selftests for separate
tables wouldn't be needed.
add/remove: 0/0 grow/shrink: 3/1 up/down: 100/-7 (93)
Function old new delta
intel_engines 160 224 +64
__func__ 13891 13910 +19
intel_engines_init_mmio 1247 1264 +17
intel_init_bsd_ring_buffer 142 135 -7
Total: Before=1479626, After=1479719, chg +0.01%
Total growth is 93, which is less then your estimation for the growth
introduced by replicating the table.
But on the other hand your solution might be more future proof. So I
don't know. Use the crystal ball to decide? :)
I think we should expect that the total engine count could grow with
future gens. In this case to me adding a new entry to a unified table
seems much cleaner (and uses less data) than adding a completely new
table each time.
Okay I was off in my estimates. But in general I was coming from the
angle of thinking that every new mmio base difference in this scheme
grows the size for all engines. So if just VCS grows one new base,
impact is multiplied by NUM_ENGINES. But maybe separate tables are also
not a solution. Perhaps pulling out mmio_base arrays to outside struct
engine_info in another set of static tables, so they could be null
terminated would be best of both worlds?
struct engine_mmio_base {
u32 gen : 8;
u32 base : 24;
};
static const struct engine_mmio_base vcs0_mmio_bases[] = {
{ .gen = 11, .base = GEN11_BSD_RING_BASE },
{ .gen = 6, .base = GEN6_BSD_RING_BASE },
{ .gen = 4, .base = BSD_RING_BASE },
{ },
};
And then in intel_engines array, for BSD:
{
...
.mmio_bases = &vcs0_mmio_bases;
...
},
This way we limit data growth only to engines which change their mmio
bases frequently.
Just an idea.
Regards,
Tvrtko
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