Slow memory access when using OpenCL without X11
Lauri Ehrenpreis
laurioma at gmail.com
Tue Mar 12 21:31:03 UTC 2019
However it's not only related to mclk and sclk. I tried this:
rocm-smi --setsclk 2
rocm-smi --setmclk 3
rocm-smi
======================== ROCm System Management Interface
========================
================================================================================================
GPU Temp AvgPwr SCLK MCLK PCLK Fan Perf
PwrCap SCLK OD MCLK OD GPU%
GPU[0] : WARNING: Empty SysFS value: pclk
GPU[0] : WARNING: Unable to read
/sys/class/drm/card0/device/gpu_busy_percent
0 34.0c N/A 1240Mhz 1333Mhz N/A 0% manual N/A
0% 0% N/A
================================================================================================
======================== End of ROCm SMI Log
========================
./cl_slow_test 1
got 1 platforms 1 devices
speed 3919.777100 avg 3919.777100 mbytes/s
speed 3809.373291 avg 3864.575195 mbytes/s
speed 585.796814 avg 2771.649170 mbytes/s
speed 188.721848 avg 2125.917236 mbytes/s
speed 188.916367 avg 1738.517090 mbytes/s
So despite forcing max sclk and mclk the memory speed is still slow..
--
Lauri
On Tue, Mar 12, 2019 at 11:21 PM Lauri Ehrenpreis <laurioma at gmail.com>
wrote:
> IN the case when memory is slow, the rocm-smi outputs this:
> ======================== ROCm System Management Interface
> ========================
>
> ================================================================================================
> GPU Temp AvgPwr SCLK MCLK PCLK Fan Perf
> PwrCap SCLK OD MCLK OD GPU%
> GPU[0] : WARNING: Empty SysFS value: pclk
> GPU[0] : WARNING: Unable to read
> /sys/class/drm/card0/device/gpu_busy_percent
> 0 30.0c N/A 400Mhz 933Mhz N/A 0% auto N/A
> 0% 0% N/A
>
> ================================================================================================
> ======================== End of ROCm SMI Log
> ========================
>
> normal memory speed case gives following:
> ======================== ROCm System Management Interface
> ========================
>
> ================================================================================================
> GPU Temp AvgPwr SCLK MCLK PCLK Fan Perf
> PwrCap SCLK OD MCLK OD GPU%
> GPU[0] : WARNING: Empty SysFS value: pclk
> GPU[0] : WARNING: Unable to read
> /sys/class/drm/card0/device/gpu_busy_percent
> 0 35.0c N/A 400Mhz 1200Mhz N/A 0% auto N/A
> 0% 0% N/A
>
> ================================================================================================
> ======================== End of ROCm SMI Log
> ========================
>
> So there is a difference in MCLK - can this cause such a huge slowdown?
>
> --
> Lauri
>
> On Tue, Mar 12, 2019 at 6:39 PM Kuehling, Felix <Felix.Kuehling at amd.com>
> wrote:
>
>> [adding the list back]
>>
>> I'd suspect a problem related to memory clock. This is an APU where
>> system memory is shared with the CPU, so if the SMU changes memory
>> clocks that would affect CPU memory access performance. If the problem
>> only occurs when OpenCL is running, then the compute power profile could
>> have an effect here.
>>
>> Laurie, can you monitor the clocks during your tests using rocm-smi?
>>
>> Regards,
>> Felix
>>
>> On 2019-03-11 1:15 p.m., Tom St Denis wrote:
>> > Hi Lauri,
>> >
>> > I don't have ROCm installed locally (not on that team at AMD) but I
>> > can rope in some of the KFD folk and see what they say :-).
>> >
>> > (in the mean time I should look into installing the ROCm stack on my
>> > Ubuntu disk for experimentation...).
>> >
>> > Only other thing that comes to mind is some sort of stutter due to
>> > power/clock gating (or gfx off/etc). But that typically affects the
>> > display/gpu side not the CPU side.
>> >
>> > Felix: Any known issues with Raven and ROCm interacting over memory
>> > bus performance?
>> >
>> > Tom
>> >
>> > On Mon, Mar 11, 2019 at 12:56 PM Lauri Ehrenpreis <laurioma at gmail.com
>> > <mailto:laurioma at gmail.com>> wrote:
>> >
>> > Hi!
>> >
>> > The 100x memory slowdown is hard to belive indeed. I attached the
>> > test program with my first e-mail which depends only on
>> > rocm-opencl-dev package. Would you mind compiling it and checking
>> > if it slows down memory for you as well?
>> >
>> > steps:
>> > 1) g++ cl_slow_test.cpp -o cl_slow_test -I
>> > /opt/rocm/opencl/include/ -L /opt/rocm/opencl/lib/x86_64/ -lOpenCL
>> > 2) logout from desktop env and disconnect hdmi/diplayport etc
>> > 3) log in over ssh
>> > 4) run the program ./cl_slow_test 1
>> >
>> > For me it reproduced even without step 2 as well but less
>> > reliably. moving mouse for example could make the memory speed
>> > fast again.
>> >
>> > --
>> > Lauri
>> >
>> >
>> >
>> > On Mon, Mar 11, 2019 at 6:33 PM Tom St Denis <tstdenis82 at gmail.com
>> > <mailto:tstdenis82 at gmail.com>> wrote:
>> >
>> > Hi Lauri,
>> >
>> > There's really no connection between the two other than they
>> > run in the same package. I too run a 2400G (as my
>> > workstation) and I got the same ~6.6GB/sec transfer rate but
>> > without a CL app running ... The only logical reason is your
>> > CL app is bottlenecking the APUs memory bus but you claim
>> > "simply opening a context is enough" so something else is
>> > going on.
>> >
>> > Your last reply though says "with it running in the
>> > background" so it's entirely possible the CPU isn't busy but
>> > the package memory controller (shared between both the CPU and
>> > GPU) is busy. For instance running xonotic in a 1080p window
>> > on my 4K display reduced the memory test to 5.8GB/sec and
>> > that's hardly a heavy memory bound GPU app.
>> >
>> > The only other possible connection is the GPU is generating so
>> > much heat that it's throttling the package which is also
>> > unlikely if you have a proper HSF attached (I use the ones
>> > that came in the retail boxes).
>> >
>> > Cheers,
>> > Tom
>> >
>>
>
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