[PATCH 1/3] drm/amdgpu: Warn when bad pages approaches 90% threshold

[Luben Tuikov]

On 2021-10-20 17:50, Felix Kuehling wrote:
> On 2021-10-20 12:35 p.m., Kent Russell wrote:
>> Currently dmesg doesn't warn when the number of bad pages approaches the
>> threshold for page retirement. WARN when the number of bad pages
>> is at 90% or greater for easier checks and planning, instead of waiting
>> until the GPU is full of bad pages
>>
>> Cc: Luben Tuikov <luben.tuikov at amd.com>
>> Cc: Mukul Joshi <Mukul.Joshi at amd.com>
>> Signed-off-by: Kent Russell <kent.russell at amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_ras_eeprom.c | 17 +++++++++++++++++
>>   1 file changed, 17 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ras_eeprom.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ras_eeprom.c
>> index f4c05ff4b26c..1ede0f0d6f55 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ras_eeprom.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ras_eeprom.c
>> @@ -1071,12 +1071,29 @@ int amdgpu_ras_eeprom_init(struct amdgpu_ras_eeprom_control *control,
>>   	control->ras_fri = RAS_OFFSET_TO_INDEX(control, hdr->first_rec_offset);
>>   
>>   	if (hdr->header == RAS_TABLE_HDR_VAL) {
>> +		int threshold = 0;
> ras->bad_page_cnt_threshold is uint32_t. I'd recommend using the same 
> type. Also add an empty line after the declaration to avoid a checkpatch 
> warning.
>
>
>>   		DRM_DEBUG_DRIVER("Found existing EEPROM table with %d records",
>>   				 control->ras_num_recs);
>>   		res = __verify_ras_table_checksum(control);
>>   		if (res)
>>   			DRM_ERROR("RAS table incorrect checksum or error:%d\n",
>>   				  res);
>> +
>> +		/* threshold = 0 means that page retirement is disabled, while
>> +		 * threshold = -1 means default behaviour
>> +		 */
>> +		if (amdgpu_bad_page_threshold == -1)
>> +			threshold = ras->bad_page_cnt_threshold;
>> +		else if (amdgpu_bad_page_threshold > 0)
>> +			threshold = amdgpu_bad_page_threshold;
>> +
>> +		/* Since multiplcation is transitive, a = 9b/10 is the same
>> +		 * as 10a = 9b. Use this for our 90% limit to avoid rounding
>> +		 */
>> +		if (threshold > 0 && ((control->ras_num_recs * 10) >= (threshold * 9)))
> Not sure how big these values can get, but you may need to cast to 
> (uint64_t) before the multiplications to avoid overflows. Alternatively 
> you could use (control->ras_num_recs / 9 >= threshold / 10). It'll 
> round, but never overflow.

I sincerely hope that by the time those values overflow multiplication by 10, AI has taken over the planet. :-)
Avoiding rounding is preferable, since we deal with integers, and for small pages... could we get 0s after division? (if the page limit is 1 :-) )
(I think squashing numbers less than 10 to 0 is a bad idea, so as not to get false positives here on small numbers.)

Even for a 32-bit word size: can we be within 3 bits of 2^32? A value of 2^29? That's a lot of pages! Actually the number of pages of VRAM is *a lot smaller* than the number of pages we fit in a typical EEPROM we put with our parts. I think we're safe.

>
>
>> +			DRM_WARN("RAS records:%u exceeds 90%% of threshold:%d",
> Nitpick: I'd add space after the two colons for readability. The 
> threshold should use %u if you make it uint32_t. This can never be negative.

Aha, so that's exactly what I like "word:%q word:%q word:%q", so when I read it in the log, my eyes scan over it, on the spaces in between the word blocks. I prefer no spaces after the colon, so as to make scanning blocks (one has to squint to see it).

Regards,
Luben


>
> Regards,
>    Felix
>
>
>> +					control->ras_num_recs,
>> +					threshold);
>>   	} else if (hdr->header == RAS_TABLE_HDR_BAD &&
>>   		   amdgpu_bad_page_threshold != 0) {
>>   		res = __verify_ras_table_checksum(control);