> Il giorno 21 mag 2019, alle ore 15:20, Paolo Valente <paolo.valente@linaro.org> ha scritto:
> 
> 
> 
>> Il giorno 21 mag 2019, alle ore 13:25, Paolo Valente <paolo.valente@linaro.org> ha scritto:
>> 
>> 
>> 
>>> Il giorno 20 mag 2019, alle ore 12:19, Paolo Valente <paolo.valente@linaro.org> ha scritto:
>>> 
>>> 
>>> 
>>>> Il giorno 18 mag 2019, alle ore 22:50, Srivatsa S. Bhat <srivatsa@csail.mit.edu> ha scritto:
>>>> 
>>>> On 5/18/19 11:39 AM, Paolo Valente wrote:
>>>>> I've addressed these issues in my last batch of improvements for BFQ,
>>>>> which landed in the upcoming 5.2. If you give it a try, and still see
>>>>> the problem, then I'll be glad to reproduce it, and hopefully fix it
>>>>> for you.
>>>>> 
>>>> 
>>>> Hi Paolo,
>>>> 
>>>> Thank you for looking into this!
>>>> 
>>>> I just tried current mainline at commit 72cf0b07, but unfortunately
>>>> didn't see any improvement:
>>>> 
>>>> dd if=/dev/zero of=/root/test.img bs=512 count=10000 oflag=dsync
>>>> 
>>>> With mq-deadline, I get:
>>>> 
>>>> 5120000 bytes (5.1 MB, 4.9 MiB) copied, 3.90981 s, 1.3 MB/s
>>>> 
>>>> With bfq, I get:
>>>> 5120000 bytes (5.1 MB, 4.9 MiB) copied, 84.8216 s, 60.4 kB/s
>>>> 
>>> 
>>> Hi Srivatsa,
>>> thanks for reproducing this on mainline.  I seem to have reproduced a
>>> bonsai-tree version of this issue.
>> 
>> Hi again Srivatsa,
>> I've analyzed the trace, and I've found the cause of the loss of
>> throughput in on my side.  To find out whether it is the same cause as
>> on your side, I've prepared a script that executes your test and takes
>> a trace during the test.  If ok for you, could you please
>> - change the value for the DEVS parameter in the attached script, if
>> needed
>> - execute the script
>> - send me the trace file that the script will leave in your working
>> dir
>> 
> 
> Sorry, I forgot to add that I also need you to, first, apply the
> attached patch (it will make BFQ generate the log I need).
> 

Sorry again :) This time for attaching one more patch.  This is
basically a blind fix attempt, based on what I see in my VM.

So, instead of only sending me a trace, could you please:
1) apply this new patch on top of the one I attached in my previous email
2) repeat your test and report results
3) regardless of whether bfq performance improves, take a trace with
   my script (I've attached a new version that doesn't risk to output an
   annoying error message as the previous one)

Thanks,
Paolo