I am not an expert on the Cache related thing, basically constant cache is part
of the Read-only cache lies in L3.
From the code in src/intel/intel_gpgpu.c, below logic is for IvyBridge:
If (slmMode)
allocate 64KB constant cache
Else
Allocate 32KB constant cache
I am not sure is there any big performance difference between less than or
greater than the real constant cache size in L3.
I simply wrote a random-selected number 512KB as the up limit in driver API.
But it did deserve to investigate the performance change according to used
constant size.
If we use too much constant larger than the constant cache allocated from L3,
I think it will definitely cause constant cache data swap in-out frequently.
Right?
If you would like to contribute any performance test to beignet, or any other
open source test suite, it would be really appreciated!
Thanks!
Ruiling
From: Beignet [mailto:[email protected]] On Behalf Of Tony
Moore
Sent: Wednesday, November 26, 2014 6:45 AM
To: [email protected]
Subject: Re: [Beignet] Combine Loads from __constant space
Another question I had about __constant, was there seems to be no limit. I'm
using __constant for every read-only parameter now totalling 1500Kb and this
test now runs in 32ms. So, is there a limit? Is this method reliable? Can
driver do this implicitly on all read-only buffers?
thanks
On Tue Nov 25 2014 at 2:11:26 PM Tony Moore
<[email protected]<mailto:[email protected]>> wrote:
Hello,
I notice that reads are not being combined when I use __constant on a read-only
kernel buffer. Is this something that can be improved?
In my kernel there are many loads from a read-only data structure. When I use
the __global specifier for the memory space I see a total of 33 send
instructions and a runtime of 81ms. When I use the __constant specifier, I see
43 send instructions and a runtime of 40ms. I'm hoping that combining the loads
could improve performance further.
thanks!
tony
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