Re: [committed] amdgcn: Ensure gfx11 is running in cumode

[Andrew Stubbs <ams@baylibre.com>]

On 22/03/2024 11:56, Thomas Schwinge wrote:
> Hi Andrew!
> 
> On 2024-03-21T13:39:53+0000, Andrew Stubbs <ams@baylibre.com> wrote:
>> CUmode "on" is the setting for compatibility with GCN and CDNA devices.
> 
>> --- a/gcc/config/gcn/gcn-hsa.h
>> +++ b/gcc/config/gcn/gcn-hsa.h
>> @@ -107,6 +107,7 @@ extern unsigned int gcn_local_sym_hash (const char *name);
>>   		  "%{" NO_XNACK XNACKOPT "} " \
>>   		  "%{" NO_SRAM_ECC SRAMOPT "} " \
>>   		  "%{march=gfx1030|march=gfx1100:-mattr=+wavefrontsize64} " \
>> +		  "%{march=gfx1030|march=gfx1100:-mattr=+cumode} " \
>>   		  "-filetype=obj"
> 
> Is this just general housekeeping, or should I be seeing any kind of
> change in the GCN target '-march=gfx1100' test results?  (I'm not.)

I'm pretty sure cumode is the default, but defaults can change and now 
we're future-proof. The option doesn't change the ELF flags at all.

The opposite of cumode allows more than 16 wavefronts in a workgroup, 
but they can't physically share a single LDS memory so it would break 
OpenACC broadcasting and reductions, and OpenMP libgomp team metadata. 
Also "cgroup" low-latency memory allocation.

Andrew