linux-kernel - Re: [PATCH v2 0/6] RFC: gup+dma: tracking dma-pinned pages

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Date:   Wed, 28 Nov 2018 08:59:01 -0500
From:   Tom Talpey <tom@...pey.com>
To:     John Hubbard <jhubbard@...dia.com>, john.hubbard@...il.com,
        linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2 0/6] RFC: gup+dma: tracking dma-pinned pages

On 11/27/2018 9:52 PM, John Hubbard wrote:
> On 11/27/18 5:21 PM, Tom Talpey wrote:
>> On 11/21/2018 5:06 PM, John Hubbard wrote:
>>> On 11/21/18 8:49 AM, Tom Talpey wrote:
>>>> On 11/21/2018 1:09 AM, John Hubbard wrote:
>>>>> On 11/19/18 10:57 AM, Tom Talpey wrote:
> [...]
>>>>
>>>> What I'd really like to see is to go back to the original fio parameters
>>>> (1 thread, 64 iodepth) and try to get a result that gets at least close
>>>> to the speced 200K IOPS of the NVMe device. There seems to be something
>>>> wrong with yours, currently.
>>>
>>> I'll dig into what has gone wrong with the test. I see fio putting data files
>>> in the right place, so the obvious "using the wrong drive" is (probably)
>>> not it. Even though it really feels like that sort of thing. We'll see.
>>>
>>>>
>>>> Then of course, the result with the patched get_user_pages, and
>>>> compare whichever of IOPS or CPU% changes, and how much.
>>>>
>>>> If these are within a few percent, I agree it's good to go. If it's
>>>> roughly 25% like the result just above, that's a rocky road.
>>>>
>>>> I can try this after the holiday on some basic hardware and might
>>>> be able to scrounge up better. Can you post that github link?
>>>>
>>>
>>> Here:
>>>
>>>      git@...hub.com:johnhubbard/linux (branch: gup_dma_testing)
>>
>> I'm super-limited here this week hardware-wise and have not been able
>> to try testing with the patched kernel.
>>
>> I was able to compare my earlier quick test with a Bionic 4.15 kernel
>> (400K IOPS) against a similar 4.20rc3 kernel, and the rate dropped to
>> ~_375K_ IOPS. Which I found perhaps troubling. But it was only a quick
>> test, and without your change.
>>
> 
> So just to double check (again): you are running fio with these parameters,
> right?
> 
> [reader]
> direct=1
> ioengine=libaio
> blocksize=4096
> size=1g
> numjobs=1
> rw=read
> iodepth=64

Correct, I copy/pasted these directly. I also ran with size=10g because
the 1g provides a really small sample set.

There was one other difference, your results indicated fio 3.3 was used.
My Bionic install has fio 3.1. I don't find that relevant because our
goal is to compare before/after, which I haven't done yet.

Tom.

> 
> 
> 
>> Say, that branch reports it has not had a commit since June 30. Is that
>> the right one? What about gup_dma_for_lpc_2018?
>>
> 
> That's the right branch, but the AuthorDate for the head commit (only) somehow
> got stuck in the past. I just now amended that patch with a new date and pushed
> it, so the head commit now shows Nov 27:
> 
>     https://github.com/johnhubbard/linux/commits/gup_dma_testing
> 
> 
> The actual code is the same, though. (It is still based on Nov 19th's f2ce1065e767
> commit.)
> 
> 
> thanks,
>