[dm-devel] dm: submit stacked requests in irq enabled context

[Neeraj Soni]

+ Alasdair and dm-devel for awareness and inputs.


On 5/9/2017 12:26 PM, Neeraj Soni wrote:
> Hi Keith/Snitzer,
>
> I have recently started using kernel 4.4 on a Android device and ran 
> Androbench to check storage read/write performance. I found that the 
> Random Read (RR) and Random write(RW) performance with Full Disk 
> Encryption is degraded compared to no Disk Encryption. Initially i 
> thought this must the issue with the storage part used and i compared 
> the performance of similar storage part on a device that was using 
> Android with kernel 3.18. I found that with no Disk Encryption the 
> performance was equivalent to the device which was using 4.4 but with 
> Disk Encryption there was degradation in RR (~20%) and RW(10%).
>
> I then tried to compare the changes that was brought in kernel 4.4 in 
> Full Disk Encryption path. I came across the patch mentioned in 
> subject and found that now a worker thread is scheduled in 
> dm_request_fn() to process the requests instead of directly invoking 
> map_request() as was in kernel 3.18.
>
> I reverted this patch and found that the RR and RW performance was now 
> closer to what we have without Disk Encryption. From the commit 
> message i understand that this change is significant and will be 
> required for blk-mq support but have you came across such degradation 
> issue with your patch and do we have any fix for this degradation 
> available?
>
> BR,
> Neeraj Soni,
> --

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