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

[Felix Kuehling <felix.kuehling@amd.com>]

On 2021-10-20 5:50 p.m., 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@amd.com>
>> Cc: Mukul Joshi <Mukul.Joshi@amd.com>
>> Signed-off-by: Kent Russell <kent.russell@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.

Ignore this comment. If you follow Luben's recommendation to check 
ras->bad_page_cnt_threshold instead of the raw module parameter, the 
limit is small enough that multiplication will never overflow.

Regards,
   Felix


>
>
>> +            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.
>
> 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);