Re: [PATCH 3/4] target/user: Introduce data_bitmap, replace data_length/data_head/data_tail

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On Fri, Feb 26, 2016 at 11:38 AM, Andy Grover <agrover@xxxxxxxxxx> wrote:
> On 02/25/2016 06:03 PM, Sheng Yang wrote:
>>>>>
>>>>> -#define DATA_SIZE (257 * 4096)
>>>>> +#define DATA_SIZE (DATA_BLOCK_BITS * DATA_BLOCK_SIZE)
>>>>
>>>>
>>>>
>>>> So the reason this was 25*7* was because in testing I saw repeated
>>>> lengths
>>>> of size 512KiB, and due to the ring not being able to be completely used
>>>> (a
>>>> limitation of the circular buffer logic) this would result in only one
>>>> request and the second having to wait. Another page allowed 2 to fit at
>>>> once
>>>> :) so now that we're not using a ring any more this can probably just be
>>>> 256
>>>> and still fit 2 512KiB allocations.
>>>>
>>>
>>> Sure. Would update.
>>
>>
>> In fact I just run another test again 256 * 4096, and found there are
>> many requests just 1MB long. So the following warning is triggered:
>>
>> "TCMU: Request of size 4160/1048576 may be too big for 65408/1048576
>> cmd/data ring buffers."
>>
>> Probably we want to increase the buffer size a bit?
>>
>> But also it shows that we cannot accommodate all the upper layer
>> request in the buffer... There is no way we can allocate 1MB buffer
>> for each request.
>
>
> I thought we could allocate an exactly 1MB buffer, with your changes, no?
> That warning message may need to be changed.

Yes we can, it make sense to remove the warning message.

Though I am not quite comfortable with one request fill the whole
buffer, because we would only able to handle one request with the
whole ring.

Like we discussed in
http://comments.gmane.org/gmane.linux.scsi.target.devel/11107 , we
should have a ring buffer fits all requests from upper layer.

--Sheng


>
> -- Andy
>
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