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

Tom Talpey
2018-11-30T02:30:16Z

On 11/29/2018 9:21 PM, John Hubbard wrote:
> On 11/29/18 6:18 PM, Tom Talpey wrote:
>> On 11/29/2018 8:39 PM, John Hubbard wrote:
>>> On 11/28/18 5:59 AM, Tom Talpey wrote:
>>>> 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:
>>>>> [...]
>>>>>> 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.
>>>>
>>>
>>> OK, the 50 MB/s was due to my particular .config. I had some expensive debug options
>>> set in mm, fs and locking subsystems. Turning those off, I'm back up to the rated
>>> speed of the Samsung NVMe device, so now we should have a clearer picture of the
>>> performance that real users will see.
>>
>> Oh, good! I'm especially glad because I was having a heck of a time
>> reconfiguring the one machine I have available for this.
>>
>>> Continuing on, then: running a before and after test, I don't see any significant
>>> difference in the fio results:
>>
>> Excerpting from below:
>>
>>> Baseline 4.20.0-rc3 (commit f2ce1065e767), as before:
>>>      read: IOPS=193k, BW=753MiB/s (790MB/s)(1024MiB/1360msec)
>>>     cpu          : usr=16.26%, sys=48.05%, ctx=251258, majf=0, minf=73
>>
>> vs
>>
>>> With patches applied:
>>>      read: IOPS=193k, BW=753MiB/s (790MB/s)(1024MiB/1360msec)
>>>     cpu          : usr=16.26%, sys=48.05%, ctx=251258, majf=0, minf=73
>>
>> Perfect results, not CPU limited, and full IOPS.
>>
>> Curiously identical, so I trust you've checked that you measured
>> both targets, but if so, I say it's good.
>>
>
> Argh, copy-paste error in the email. The real "before" is ever so slightly
> better, at 194K IOPS and 759 MB/s:

Definitely better - note the system CPU is lower, which is probably the
reason for the increased IOPS.

> cpu : usr=18.24%, sys=44.77%, ctx=251527, majf=0, minf=73

Good result - a correct implementation, and faster.

Tom.

>
> $ fio ./experimental-fio.conf
> reader: (g=0): rw=read, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=64
> fio-3.3
> Starting 1 process
> Jobs: 1 (f=1)
> reader: (groupid=0, jobs=1): err= 0: pid=1715: Thu Nov 29 17:07:09 2018
> read: IOPS=194k, BW=759MiB/s (795MB/s)(1024MiB/1350msec)
> slat (nsec): min=1245, max=2812.7k, avg=1538.03, stdev=5519.61
> clat (usec): min=148, max=755, avg=326.85, stdev=18.13
> lat (usec): min=150, max=3483, avg=328.41, stdev=19.53
> clat percentiles (usec):
> | 1.00th=[ 322], 5.00th=[ 326], 10.00th=[ 326], 20.00th=[ 326],
> | 30.00th=[ 326], 40.00th=[ 326], 50.00th=[ 326], 60.00th=[ 326],
> | 70.00th=[ 326], 80.00th=[ 326], 90.00th=[ 326], 95.00th=[ 326],
> | 99.00th=[ 355], 99.50th=[ 537], 99.90th=[ 553], 99.95th=[ 553],
> | 99.99th=[ 619]
> bw ( KiB/s): min=767816, max=783096, per=99.84%, avg=775456.00, stdev=10804.59, samples=2
> iops : min=191954, max=195774, avg=193864.00, stdev=2701.15, samples=2
> lat (usec) : 250=0.09%, 500=99.30%, 750=0.61%, 1000=0.01%
> cpu : usr=18.24%, sys=44.77%, ctx=251527, majf=0, minf=73
> IO depths : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=0.1%, >=64=100.0%
> submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
> complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.1%, >=64=0.0%
> issued rwts: total=262144,0,0,0 short=0,0,0,0 dropped=0,0,0,0
> latency : target=0, window=0, percentile=100.00%, depth=64
>
> Run status group 0 (all jobs):
> READ: bw=759MiB/s (795MB/s), 759MiB/s-759MiB/s (795MB/s-795MB/s), io=1024MiB (1074MB), run=1350-1350msec
>
> Disk stats (read/write):
> nvme0n1: ios=222853/0, merge=0/0, ticks=71410/0, in_queue=71935, util=100.00%
>
> thanks,
>