[igt-dev] [PATCH i-g-t] tests/perf_pmu: Compare against requested freq in frequency subtest
Tvrtko Ursulin
tvrtko.ursulin at linux.intel.com
Fri Dec 23 09:22:53 UTC 2022
On 22/12/2022 20:28, Rodrigo Vivi wrote:
> On Mon, Dec 19, 2022 at 08:46:59AM +0000, Tvrtko Ursulin wrote:
>>
>> On 17/12/2022 02:49, Dixit, Ashutosh wrote:
>>> On Fri, 16 Dec 2022 07:39:52 -0800, Rodrigo Vivi wrote:
>>>> On Fri, Dec 16, 2022 at 09:37:31AM +0000, Tvrtko Ursulin wrote:
>>>>>
>>>>> On 16/12/2022 06:21, Dixit, Ashutosh wrote:
>>>>>> On Thu, 24 Nov 2022 04:42:08 -0800, Tvrtko Ursulin wrote:
>>>>>>>
>>>>>>> On 23/11/2022 06:03, Dixit, Ashutosh wrote:
>>>>>>>> On Mon, 21 Nov 2022 01:09:55 -0800, Tvrtko Ursulin wrote:
>>>>>>>>>
>>>>>>>>
>>>>>>
>>>>>> Hi Tvrtko,
>>>>>>
>>>>>> Sorry for the delay in replying on this. We are discussing this but still
>>>>>> no conclusion. I have replied what I can below, will update again after I
>>>>>> know more. Wanted to send a reply before disappearing for the
>>>>>> holidays. Please see below.
>>>>>>
>>>>>>>> Hi Tvrtko,
>>>>>>>>
>>>>>>>> I am only offering an overall clarification below first, not answering all
>>>>>>>> of your points for now.
>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 19/11/2022 02:00, Ashutosh Dixit wrote:
>>>>>>>>>> With SLPC, even when we set the same min and max freq's, the requested and
>>>>>>>>>> actual freq's can differ from the min/max freq set. For example "efficient
>>>>>>>>>> freq" (when in effect) can override set min/max freq. In general FW is the
>>>>>>>>>> final arbiter in determining freq and can override set values.
>>>>>>>>>>
>>>>>>>>>> Therefore in igt at perf_pmu@frequency subtest, compare the requested freq
>>>>>>>>>> reported by PMU not against the set freq's but against the requested freq
>>>>>>>>>> reported in sysfs. Also add a delay after setting freq's to account for
>>>>>>>>>> messaging delays in setting freq's in GuC.
>>>>>>>>>>
>>>>>>>>>> v2: Introduce a 100 ms delay after setting freq
>>>>>>>>>> v3: Update commit message, code identical to v2
>>>>>>>>>>
>>>>>>>>>> Bug: https://gitlab.freedesktop.org/drm/intel/-/issues/6806
>>>>>>>>>> Cc: Vinay Belgaumkar <vinay.belgaumkar at intel.com>
>>>>>>>>>> Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
>>>>>>>>>> Signed-off-by: Ashutosh Dixit <ashutosh.dixit at intel.com>
>>>>>>>>>> ---
>>>>>>>>>> tests/i915/perf_pmu.c | 23 +++++++++++++++--------
>>>>>>>>>> 1 file changed, 15 insertions(+), 8 deletions(-)
>>>>>>>>>>
>>>>>>>>>> diff --git a/tests/i915/perf_pmu.c b/tests/i915/perf_pmu.c
>>>>>>>>>> index f363db2ba13..02f6ae989b1 100644
>>>>>>>>>> --- a/tests/i915/perf_pmu.c
>>>>>>>>>> +++ b/tests/i915/perf_pmu.c
>>>>>>>>>> @@ -1543,10 +1543,13 @@ test_interrupts_sync(int gem_fd)
>>>>>>>>>> igt_assert_lte(target, busy);
>>>>>>>>>> }
>>>>>>>>>> +/* Wait for GuC SLPC freq changes to take effect */
>>>>>>>>>> +#define wait_freq_set() usleep(100000)
>>>>>>>>>
>>>>>>>>> A future task of maybe adding a drop_caches flag to wait for this?
>>>>>>>>>
>>>>>>>>> Alternatively, if we have a sysfs or debugfs file which reflects the value
>>>>>>>>> once GuC has processed it, keep reading it until it is updated? Even if to
>>>>>>>>> something other than it was before the write, to handle the inability to
>>>>>>>>> set the exact requested frequency sometimes?
>>>>>>>>>>
>>>>>>>>>> +
>>>>>>>>>> static void
>>>>>>>>>> test_frequency(int gem_fd)
>>>>>>>>>> {
>>>>>>>>>> - uint32_t min_freq, max_freq, boost_freq;
>>>>>>>>>> + uint32_t min_freq, max_freq, boost_freq, min_req, max_req;
>>>>>>>>>> uint64_t val[2], start[2], slept;
>>>>>>>>>> double min[2], max[2];
>>>>>>>>>> igt_spin_t *spin;
>>>>>>>>>> @@ -1572,10 +1575,11 @@ test_frequency(int gem_fd)
>>>>>>>>>> * Set GPU to min frequency and read PMU counters.
>>>>>>>>>> */
>>>>>>>>>> igt_require(igt_sysfs_set_u32(sysfs, "gt_min_freq_mhz", min_freq));
>>>>>>>>>> - igt_require(igt_sysfs_get_u32(sysfs, "gt_min_freq_mhz") == min_freq);
>>>>>>>>>> igt_require(igt_sysfs_set_u32(sysfs, "gt_max_freq_mhz", min_freq));
>>>>>>>>>> - igt_require(igt_sysfs_get_u32(sysfs, "gt_max_freq_mhz") == min_freq);
>>>>>>>>>> igt_require(igt_sysfs_set_u32(sysfs, "gt_boost_freq_mhz", min_freq));
>>>>>>>>>> + wait_freq_set();
>>>>>>>>>> + igt_require(igt_sysfs_get_u32(sysfs, "gt_min_freq_mhz") == min_freq);
>>>>>>>>>> + igt_require(igt_sysfs_get_u32(sysfs, "gt_max_freq_mhz") == min_freq);
>>>>>>>>>> igt_require(igt_sysfs_get_u32(sysfs, "gt_boost_freq_mhz") == min_freq);
>>>>>>>>>> gem_quiescent_gpu(gem_fd); /* Idle to be sure the change takes
>>>>>>>>>> effect */
>>>>>>>>>> @@ -1587,6 +1591,7 @@ test_frequency(int gem_fd)
>>>>>>>>>> min[0] = 1e9*(val[0] - start[0]) / slept;
>>>>>>>>>> min[1] = 1e9*(val[1] - start[1]) / slept;
>>>>>>>>>> + min_req = igt_sysfs_get_u32(sysfs, "gt_cur_freq_mhz");
>>>>>>>>>
>>>>>>>>> This really leaves a bad taste for me still, sorry. First of all, it may
>>>>>>>>> make it more palatable if readback was immediately after wait_freq_set(),
>>>>>>>>> or as part of it. Otherwise it seems like even more confused test and sysfs
>>>>>>>>> ABI.
>>>>>>>>>
>>>>>>>>> Did we close on my question of whether we can make readback of
>>>>>>>>> gt_max_freq_mhz actually represent the real max? Correct me please if I got
>>>>>>>>> confused - with min freq checking here we write max=300 and get 350? If so
>>>>>>>>> can we make gt_max_freq_mhz return 350 after the write of 300? Or return an
>>>>>>>>> error?
>>>>>>>>
>>>>>>>> Did you read Vinay's email on v1 here:
>>>>>>>>
>>>>>>>> https://patchwork.freedesktop.org/patch/510304/?series=110574&rev=1#comment_921571
>>>>>>>>
>>>>>>>> As Vinay says, SLPC is requesting an entirely different freq (the effecient
>>>>>>>> freq rather than the set 'min == max freq') and no amount of waiting will
>>>>>>>> result in the requested freq being the same as the set 'min == max
>>>>>>>> freq'. Also the efficient freq cannot be controlled from user space.
>>>>>>>
>>>>>>> Why is that not a break in our ABI? What is the point in allowing users to
>>>>>>> write into this field if the desired value can be silently ignored?
>>>>>>
>>>>>> Yes, this is in discussion. FW is doing this and we need to see if FW can
>>>>>> be made to obey the i915 ABI. IMHO what matters is performance per watt and
>>>>>> if the ABI has to be tossed so be it. I will keep this list posted about
>>>>>> what happens here. Merging any patches for these issues (GL #6806 and
>>>>>> #6786) is blocked till the ABI breakage issue is resolved one way or
>>>>>> another.
>>>>>
>>>>> Two thoughts here, one has been mentioned before.
>>>>>
>>>>> New one is that performance per watt perhaps does not matter (is not a
>>>>> primary concern at least) for use cases where "users" (for some definition)
>>>>> tweak the min/max in sysfs. Presumably in those cases user wants control,
>>>>> for some reason, so as long as it is safe and within the limits why not give
>>>>> it to them.
>>>>>
>>>>> Same argument from a different angle - what is the use case for allowing
>>>>> min/max control which does not really do what it says on the tin?
>>>>>
>>>>> Old thought is this - if SLPC refuses to be controlled using our existing
>>>>> controls then we could just say -ENODEV on attempts to modify them. Whether
>>>>> for any input value, or some, depending on what SLPC can support (or wants
>>>>> to support).
>>>>
>>>> The problem is not just SLPC. The freq is ultimately decided by PCODE and it
>>>> has sudo and all the rights to disrespect what drivers (including SLPC as a
>>>> a driver from PCODE perspective) are requesting.
>>>>
>>>>>
>>>>> Important to note I am primarily focusing on the min freq here, which AFAIR
>>>>> we concluded can behave that user writes in 300, but SLPC decides it will
>>>>> only go as low as 350.
>>>>
>>>> The other caveat here with the efficient freq is that it is dynamic and PCODE
>>>> decides it with runtime conditions. It may start with 300, then move to 350,
>>>> then back to 300. i915 is only stashing the initial value.
>>>>
>>>> We could potentially update our rpe everytime any freq control is
>>>> touched.
>>>
>>> We thought of doing this but two points:
>>>
>>> 1. i915 now reads the same register as GuC for rpe but I never see the
>>> value in this register change.
>>> 2. Even if we could know the real rpe, the freq's might be set before a
>>> workload start running and rpe might change after the workload starts
>>> running. So knowing rpe before the workload might not be very useful.
>>>
>>> I am of the opposite opinion that anyway the previous kernel ABI is
>>> probably now irrecoverably bust, so we should give FW free reign and stop
>>> disabling efficient freq the way we do now when min_freq < rpe_freq.
>>
>> We have to answer the question of why we need to keep exposing the sysfs
>> controls if they don't/can't/won't do what they say on the tin. Could we
>> make a break with DG2 for instance? Some use cases might suffer but it's
>> probably better than having them think it does what they think it does, or
>> file bugs when it does not.
>
> That's a good question. But if we have no control at all people will still
> file requests for something our hardware and low level firmwares cannot promise.
>
> There are many folks who run important/critical experiments using these
> interfaces at the same time they are monitoring throttle conditions and all.
Aren't the two paragraphs a bit in contradiction? Important and critical
experiments using controls which are not doing what they think they are.
I don't claim I know for what all use cases do they get used. I *think*
there was one in the media transcoding world one where people wanted
truly fixed frequency so they can compare like-for-like between something.
So bah.. but okay for the perf_pmu changes, how about instead of this:
rpN = read RPn from sysfs
set_min_freq(rpN)
sleep
real_min = read actual from sysfs
actual = sample pmu for t
assert real_min is actual
We do this:
rpN = read RPn from sysfs
set_min_freq(rpN)
sleep
fw_min = read actual from sysfs
set_min_freq(fw_min)
sleep
actual = sample pmu for t
assert fw_min is actual
That's a tiny difference which both "documents" and verifies that even
if we cannot set the min to RPn, firmware will somewhat consistently
(stable) respect the minimum it prefers.
Is that somewhat acceptable?
Regards,
Tvrtko
More information about the igt-dev
mailing list