RE: [PATCH] drm/amdgpu: try again kiq access if not in IRQ(v2)

["Liu, Monk" <Monk.Liu-5C7GfCeVMHo@public.gmane.org>]

Hi Christian

I couln't find this "may_sleep()" in my 4.13kernel , did I miss something ??

Thanks 
/Monk

-----Original Message-----
From: Christian König [mailto:ckoenig.leichtzumerken@gmail.com] 
Sent: 2018年3月5日 19:21
To: Liu, Monk <Monk.Liu@amd.com>; Koenig, Christian <Christian.Koenig@amd.com>; Kuehling, Felix <Felix.Kuehling@amd.com>; amd-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/amdgpu: try again kiq access if not in IRQ(v2)

Am 05.03.2018 um 09:08 schrieb Liu, Monk:
> To better approach this issue I suggest to do the following:
> 1. Revert the original patch.
>
> 2. Stop waiting to long for writes. E.g. use a separate timeout (20ms
> maybe?) to wait for the write. Then do a WARN_ON_ONCE when we timeout.
> Cannot do that 20ms is not enough, sometimes you need 10 seconds since 
> other VFs may doing bad things like occupying GPU intentionally or 
> they are doing TDR, so I don't think separate read and write is good 
> idea, they should be treated equally

Well the question is if separating read&writes would actually help.

>
> 3. To the read function add a "if (!in_intterupt()) may_sleep();" and then retest. That should at least print a nice warning when called from atomic context.
> Sorry what is may_sleep() ??
>
> 4. Test the whole thing and try to fix all warnings about atomic 
> contexts from the may_sleep();
>
> 5. Reapply the original patch, but this time only for the read function, not the write function.
>
>
>  From current LKG code, the only one spin lock may wrapping the 
> kiq_rreg/wreg() is the pcie_idx_lock, and this lock is only used during init(), Since init() is run under the case of exclusive mode for SRIOV, which means:
> 1)  register access is not go through KIQ (see admgpu_mm_reg)
> 2)  those functions are only in bif_medium_grain_xxx part (vi.c and 
> nbio_v6.c) , and they won't hit under SRIOV ( we return in the head if SRIOV detect) So I don' think this spin_lock may cause trouble...

Ok in this case let's keep the patch for now, but please provide a new patch which adds "if (!in_intterupt()) may_sleep();" in both the read and write function.

This way we should at least catch problems early on.

Christian.

>
> /Monk
>
>
>
> -----Original Message-----
> From: Christian König [mailto:ckoenig.leichtzumerken@gmail.com]
> Sent: 2018年3月5日 15:57
> To: Liu, Monk <Monk.Liu@amd.com>; Koenig, Christian 
> <Christian.Koenig@amd.com>; Kuehling, Felix <Felix.Kuehling@amd.com>; 
> amd-gfx@lists.freedesktop.org
> Subject: Re: [PATCH] drm/amdgpu: try again kiq access if not in 
> IRQ(v2)
>
>> otherwise I don't see how it is better by reverting it
> Well it's better to revert it for now because it seems to create more problems than it solves.
>
> To better approach this issue I suggest to do the following:
> 1. Revert the original patch.
>
> 2. Stop waiting to long for writes. E.g. use a separate timeout (20ms
> maybe?) to wait for the write. Then do a WARN_ON_ONCE when we timeout.
>
> 3. To the read function add a "if (!in_intterupt()) may_sleep();" and then retest. That should at least print a nice warning when called from atomic context.
>
> 4. Test the whole thing and try to fix all warnings about atomic 
> contexts from the may_sleep();
>
> 5. Reapply the original patch, but this time only for the read function, not the write function.
>
> Regards,
> Christian.
>
> Am 05.03.2018 um 05:20 schrieb Liu, Monk:
>> When there are 16 VF/VM on one GPU, we can easily hit "sys lockup to 
>> 22s" kernel error/warning introduced by kiq_rreg/wreg routine That's 
>> why I must use this patch to let thread sleep a while and try again,
>>
>> If you insist reverting this patch please give me a solution, 
>> otherwise I don't see how it is better by reverting it
>>
>> /Monk
>>
>> -----Original Message-----
>> From: Christian König [mailto:ckoenig.leichtzumerken@gmail.com]
>> Sent: 2018年3月3日 21:38
>> To: Kuehling, Felix <Felix.Kuehling@amd.com>; Liu, Monk 
>> <Monk.Liu@amd.com>; amd-gfx@lists.freedesktop.org
>> Subject: Re: [PATCH] drm/amdgpu: try again kiq access if not in
>> IRQ(v2)
>>
>> Am 02.03.2018 um 21:47 schrieb Felix Kuehling:
>>> On 2018-03-02 04:29 AM, Liu, Monk wrote:
>>>> In_atomic() isnot encouraged to be used to judge if sleep is 
>>>> possible, see the macros of it
>>>>
>>>> #define in_atomic() (preept_count() != 0)
>>> OK. But my point is still that you're not testing the right thing 
>>> when you check in_interrupt(). The comment before the in_atomic 
>>> macro definition states the limitations and says "do not use in driver code".
>>> Unfortunately it doesn't suggest any alternative. I think 
>>> in_interrupt is actually worse, because it misses even more cases than in_atomic.
>> Thinking about this, Felix seems to be absolutely right.
>>
>> So we need to revert this patch since you can't reliable detect in a driver if sleeping is allowed or not.
>>
>> Regards,
>> Christian.
>>
>>> Regards,
>>>      Felix
>>>
>>>> /Monk
>>>>
>>>> -----Original Message-----
>>>> From: Kuehling, Felix
>>>> Sent: 2018年3月1日 23:50
>>>> To: amd-gfx@lists.freedesktop.org; Liu, Monk <Monk.Liu@amd.com>
>>>> Subject: Re: [PATCH] drm/amdgpu: try again kiq access if not in
>>>> IRQ(v2)
>>>>
>>>> On 2018-02-28 02:27 AM, Monk Liu wrote:
>>>>> sometimes GPU is switched to other VFs and won't swich back soon, 
>>>>> so the kiq reg access will not signal within a short period, 
>>>>> instead of busy waiting a long time(MAX_KEQ_REG_WAIT) and 
>>>>> returning TMO we can istead sleep 5ms and try again later (non irq 
>>>>> context)
>>>>>
>>>>> And since the waiting in kiq_r/weg is busy wait, so 
>>>>> MAX_KIQ_REG_WAIT shouldn't set to a long time, set it to 10ms is more appropriate.
>>>>>
>>>>> if gpu already in reset state, don't retry the KIQ reg access 
>>>>> otherwise it would always hang because KIQ was already die usually.
>>>>>
>>>>> v2:
>>>>> replace schedule() with msleep() for the wait
>>>>>
>>>>> Change-Id: I8fc807ce85a8d30d2b50153f3f3a6eda344ef994
>>>>> Signed-off-by: Monk Liu <Monk.Liu@amd.com>
>>>>> ---
>>>>>     drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c | 15 +++++++++++++--
>>>>>     1 file changed, 13 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
>>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
>>>>> index b832651..1672f5b 100644
>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
>>>>> @@ -22,7 +22,7 @@
>>>>>      */
>>>>>     
>>>>>     #include "amdgpu.h"
>>>>> -#define MAX_KIQ_REG_WAIT	100000000 /* in usecs */
>>>>> +#define MAX_KIQ_REG_WAIT	10000 /* in usecs, 10ms */
>>>>>     
>>>>>     uint64_t amdgpu_csa_vaddr(struct amdgpu_device *adev)  { @@
>>>>> -152,9
>>>>> +152,14 @@ uint32_t amdgpu_virt_kiq_rreg(struct amdgpu_device 
>>>>> +*adev, uint32_t reg)
>>>>>     	amdgpu_ring_commit(ring);
>>>>>     	spin_unlock_irqrestore(&kiq->ring_lock, flags);
>>>>>     
>>>>> +retry_read:
>>>>>     	r = amdgpu_fence_wait_polling(ring, seq, MAX_KIQ_REG_WAIT);
>>>>>     	if (r < 1) {
>>>>>     		DRM_ERROR("wait for kiq fence error: %ld\n", r);
>>>>> +		if (!in_interrupt() && !adev->in_gpu_reset) {
>>>> You should check in_atomic here. Because it's invalid to sleep in atomic context (e.g. while holding a spin lock) even when not in an interrupt.
>>>> This seems to happen a lot for indirect register access, e.g.
>>>> soc15_pcie_rreg.
>>>>
>>>> Regards,
>>>>      Felix
>>>>
>>>>> +			msleep(5);
>>>>> +			goto retry_read;
>>>>> +		}
>>>>>     		return ~0;
>>>>>     	}
>>>>>     	val = adev->wb.wb[adev->virt.reg_val_offs];
>>>>> @@ -179,9 +184,15 @@ void amdgpu_virt_kiq_wreg(struct amdgpu_device *adev, uint32_t reg, uint32_t v)
>>>>>     	amdgpu_ring_commit(ring);
>>>>>     	spin_unlock_irqrestore(&kiq->ring_lock, flags);
>>>>>     
>>>>> +retry_write:
>>>>>     	r = amdgpu_fence_wait_polling(ring, seq, MAX_KIQ_REG_WAIT);
>>>>> -	if (r < 1)
>>>>> +	if (r < 1) {
>>>>>     		DRM_ERROR("wait for kiq fence error: %ld\n", r);
>>>>> +		if (!in_interrupt() && !adev->in_gpu_reset) {
>>>>> +			msleep(5);
>>>>> +			goto retry_write;
>>>>> +		}
>>>>> +	}
>>>>>     }
>>>>>     
>>>>>     /**
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