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

From: John Hubbard <jhubbard@nvidia.com>
To: Tom Talpey <tom@talpey.com>, <john.hubbard@gmail.com>,
	<linux-mm@kvack.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-rdma <linux-rdma@vger.kernel.org>,
	<linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH v2 0/6] RFC: gup+dma: tracking dma-pinned pages
Date: Tue, 27 Nov 2018 18:52:28 -0800	[thread overview]
Message-ID: <313bf82d-cdeb-8c75-3772-7a124ecdfbd5@nvidia.com> (raw)
In-Reply-To: <15e4a0c0-cadd-e549-962f-8d9aa9fc033a@talpey.com>

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@github.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

> 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,
-- 
John Hubbard
NVIDIA