Re: [Qemu-devel] [PATCH v4 3/8] ide: account UNMAP (TRIM) operations

[Anton Nefedov]

On 8/10/2018 6:46 PM, Kevin Wolf wrote:
> Am 08.10.2018 um 17:25 hat Anton Nefedov geschrieben:
>>
>>
>> On 8/10/2018 6:03 PM, Kevin Wolf wrote:
>>> Am 08.10.2018 um 16:38 hat Anton Nefedov geschrieben:
>>>> On 4/10/2018 6:33 PM, Kevin Wolf wrote:
>>>>> Am 21.08.2018 um 11:46 hat Anton Nefedov geschrieben:
>>>>>> Signed-off-by: Anton Nefedov <address@hidden>
>>>>>> Reviewed-by: Alberto Garcia <address@hidden>
>>>>>> ---
>>>>>>     hw/ide/core.c | 12 ++++++++++++
>>>>>>     1 file changed, 12 insertions(+)
>>>>>>
>>>>>> diff --git a/hw/ide/core.c b/hw/ide/core.c
>>>>>> index 2c62efc..352429b 100644
>>>>>> --- a/hw/ide/core.c
>>>>>> +++ b/hw/ide/core.c
>>>>>> @@ -440,6 +440,14 @@ static void ide_issue_trim_cb(void *opaque, int ret)
>>>>>>         TrimAIOCB *iocb = opaque;
>>>>>>         IDEState *s = iocb->s;
>>>>>>     
>>>>>> +    if (iocb->i >= 0) {
>>>>>> +        if (ret >= 0) {
>>>>>> +            block_acct_done(blk_get_stats(s->blk), &s->acct);
>>>>>> +        } else {
>>>>>> +            block_acct_failed(blk_get_stats(s->blk), &s->acct);
>>>>>> +        }
>>>>>> +    }
>>>>>> +
>>>>>>         if (ret >= 0) {
>>>>>>             while (iocb->j < iocb->qiov->niov) {
>>>>>>                 int j = iocb->j;
>>>>>> @@ -461,6 +469,9 @@ static void ide_issue_trim_cb(void *opaque, int ret)
>>>>>>                         goto done;
>>>>>>                     }
>>>>>>     
>>>>>> +                block_acct_start(blk_get_stats(s->blk), &s->acct,
>>>>>> +                                 count << BDRV_SECTOR_BITS, 
>>>>>> BLOCK_ACCT_UNMAP);
>>>>>> +
>>>>>>                     /* Got an entry! Submit and exit.  */
>>>>>>                     iocb->aiocb = blk_aio_pdiscard(s->blk,
>>>>>>                                                    sector << 
>>>>>> BDRV_SECTOR_BITS,
>>>>>> @@ -845,6 +856,7 @@ static void ide_dma_cb(void *opaque, int ret)
>>>>>>         }
>>>>>>     
>>>>>>         if (ret == -EINVAL) {
>>>>>> +        block_acct_invalid(blk_get_stats(s->blk), BLOCK_ACCT_UNMAP);
>>>>>
>>>>> This looks wrong to me, ide_dma_cb() is not only called for unmap, but
>>>>> also for reads and writes, and each of them could return -EINVAL.
>>>>>
>>>>
>>>> Stating here BLOCK_ACCT_UNMAP is definitely a blunder :(
>>>>
>>>>> Also, -EINVAL doesn't necessarily mean that the guest driver did
>>>>> something wrong, it could also be the result of a host problem.
>>>>> Therefore, it isn't right to call block_acct_invalid() here - especially
>>>>> since the request may already have been accounted for as either done or
>>>>> failed in ide_issue_trim_cb().
>>>>>
>>>>
>>>> Couldn't be accounted done with such retcode;
>>>> and it seems I shouldnt do block_acct_failed() there anyway - or it's
>>>> accounted twice: there and in ide_dma_cb()->ide_handle_rw_error()
>>>>
>>>> But if EINVAL (from further layers) should not be accounted as an
>>>> invalid op, then it should be accounted failed instead, the thing that
>>>> current code does not do.
>>>> (and which brings us back to possible double-accounting if we account
>>>> invalid in ide_issue_trim_cb() )
>>>
>>> Yes, commit caeadbc8ba4 was already wrong in assuming that there is
>>> only one possible source for -EINVAL.
>>>
>>>>> Instead, I think it would be better to immediately account for invalid
>>>>> requests in ide_issue_trim_cb() where iocb->ret = -EINVAL is set and we
>>>>> know for sure that indeed !ide_sect_range_ok() is the cause for the
>>>>> -EINVAL return code.
>>>>>
>>>> So I guess yes, move acct_invalid in ide_issue_trim_cb() and leave
>>>> acct_failed there, and filter off TRIM commands in the common
>>>> accounting.
>>>
>>> blk_aio_discard() can fail with -EINVAL, too, so getting this error code
>>> from a TRIM command doesn't mean anything. It can still have multiple
>>> possible sources.
>>>
>>
>> I meant that common ide_dma_cb() should account EINVAL (along with other
>> errors) as failed, unless it's TRIM, which means it's already
>> accounted (either invalid or failed)
> 
> Oh, you would already account for failure in ide_issue_trim_cb(), too,
> but only if it's EINVAL? That feels like it would complicate the code
> quite a bit.
> 

No, no :) ide_issue_trim_cb does the proper accounting (failed/invalid)
for TRIM.
Then common path (ide_dma_cb()) does not account TRIM operations at all
regardless of the error code. No need to check for TRIM specifically if
we have BLOCK_ACCT_NONE.

> And actually, didn't commit caeadbc8ba4 break werror=stop for requests
> returning -EINVAL because we don't call ide_handle_rw_error() any more?
> 

Yes.

Read/write ignore werror=stop for invalid range case (not for EINVAL).
I wonder if it's crucial to ignore it for TRIM too, otherwise we could
just remove this chunk

      if (ret == -EINVAL) {
          ide_dma_error(s);
          return;
      }