Re: [SPDK] Problem with Blobstore when write 65MB continously

[Luse, Paul E <paul.e.luse at intel.com>]

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Hi Zhang,

I'm not suggesting changing anything right now, thanks for the point on the SSD though - I'd wait for Ben or someone else to jump in with a bit more info on why this is happening.

Thanks!!
Paul

-----Original Message-----
From: Zhengyu Zhang [mailto:freeman.zhang1992(a)gmail.com] 
Sent: Wednesday, January 10, 2018 9:00 AM
To: Luse, Paul E <paul.e.luse(a)intel.com>
Cc: Storage Performance Development Kit <spdk(a)lists.01.org>
Subject: Re: [SPDK] Problem with Blobstore when write 65MB continously

Hi Paul

Thanks for your reply!


On 1/10/18 11:18 PM, Luse, Paul E wrote:
> So what’s happening here is internally within Blobstore when
> _spdk_blob_request_submit_op() tries to get a channel->req via
> spdk_bs_batch_open() for a write (bear the end) it doesn’t have any 
> available so returns NULL which results in a callback error of –ENOMEM 
> to the hello_blob callback.  The default number of channel reqs is 512 
> and the hello_blob app doesn’t change that and uses a single channel 
> for submitting the 520 back to back write requests that you are 
> issuing and this failure happens right there towards the end.
> 

So you are suggesting me to tune the number of channel reqs or using multiple channels if I want to write more?

> 
> Ben, if I crank up the max channel reqs this works OK.  I’m thinking 
> this shouldn’t be needed and wondering why we aren’t placing completed 
> channel reqs back on the list fast enough (if that’s the real problem).
> Something to do with this being a malloc backend maybe?  Would try 
> w/nvme but my dev system isn’t quite ready for prime time yet after 
> reblasting it….
> 
>

I tested on both malloc backend and an P3700 NVMe SSD. Their results are the same.

Thanks!
Zhengyu