On 11/5/18 1:54 AM, Jan Kara wrote: > On Sun 04-11-18 23:10:12, John Hubbard wrote: >> On 10/13/18 9:47 AM, Christoph Hellwig wrote: >>> On Sat, Oct 13, 2018 at 12:34:12AM -0700, John Hubbard wrote: >>>> In patch 6/6, pin_page_for_dma(), which is called at the end of get_user_pages(), >>>> unceremoniously rips the pages out of the LRU, as a prerequisite to using >>>> either of the page->dma_pinned_* fields. >>>> >>>> The idea is that LRU is not especially useful for this situation anyway, >>>> so we'll just make it one or the other: either a page is dma-pinned, and >>>> just hanging out doing RDMA most likely (and LRU is less meaningful during that >>>> time), or it's possibly on an LRU list. >>> >>> Have you done any benchmarking what this does to direct I/O performance, >>> especially for small I/O directly to a (fast) block device? >>> >> >> Hi Christoph, >> >> I'm seeing about 20% slower in one case: lots of reads and writes of size 8192 B, >> on a fast NVMe device. My put_page() --> put_user_page() conversions are incomplete >> and buggy yet, but I've got enough of them done to briefly run the test. >> >> One thing that occurs to me is that jumping on and off the LRU takes time, and >> if we limited this to 64-bit platforms, maybe we could use a real page flag? I >> know that leaves 32-bit out in the cold, but...maybe use this slower approach >> for 32-bit, and the pure page flag for 64-bit? uggh, we shouldn't slow down anything >> by 20%. >> >> Test program is below. I hope I didn't overlook something obvious, but it's >> definitely possible, given my lack of experience with direct IO. >> >> I'm preparing to send an updated RFC this week, that contains the feedback to date, >> and also many converted call sites as well, so that everyone can see what the whole >> (proposed) story would look like in its latest incarnation. > > Hmm, have you tried larger buffer sizes? Because synchronous 8k IO isn't > going to max-out NVME iops by far. Can I suggest you install fio [1] (it > has the advantage that it is pretty much standard for a test like this so > everyone knows what the test does from a glimpse) and run with it something > like the following workfile: > > [reader] > direct=1 > ioengine=libaio > blocksize=4096 > size=1g > numjobs=1 > rw=read > iodepth=64 > > And see how the numbers with and without your patches compare? > > Honza > > [1] https://github.com/axboe/fio That program is *very* good to have. Whew. Anyway, it looks like read bandwidth is approximately 74 MiB/s with my patch (it varies a bit, run to run), as compared to around 85 without the patch, so still showing about a 20% performance degradation, assuming I'm reading this correctly. Raw data follows, using the fio options you listed above: Baseline (without my patch): ---------------------------- 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): [R(1)][100.0%][r=87.2MiB/s,w=0KiB/s][r=22.3k,w=0 IOPS][eta 00m:00s] reader: (groupid=0, jobs=1): err= 0: pid=1775: Mon Nov 5 12:08:45 2018 read: IOPS=21.9k, BW=85.7MiB/s (89.9MB/s)(1024MiB/11945msec) slat (usec): min=13, max=3855, avg=44.17, stdev=61.18 clat (usec): min=71, max=13093, avg=2869.40, stdev=1225.23 lat (usec): min=179, max=14003, avg=2913.65, stdev=1241.75 clat percentiles (usec): | 1.00th=[ 2311], 5.00th=[ 2343], 10.00th=[ 2343], 20.00th=[ 2343], | 30.00th=[ 2343], 40.00th=[ 2376], 50.00th=[ 2376], 60.00th=[ 2376], | 70.00th=[ 2409], 80.00th=[ 2933], 90.00th=[ 4359], 95.00th=[ 5276], | 99.00th=[ 8291], 99.50th=[ 9110], 99.90th=[10945], 99.95th=[11469], | 99.99th=[12256] bw ( KiB/s): min=80648, max=93288, per=99.80%, avg=87608.57, stdev=3201.35, samples=23 iops : min=20162, max=23322, avg=21902.09, stdev=800.37, samples=23 lat (usec) : 100=0.01%, 250=0.01%, 500=0.01%, 750=0.01%, 1000=0.01% lat (msec) : 2=0.02%, 4=88.47%, 10=11.27%, 20=0.25% cpu : usr=2.68%, sys=94.68%, ctx=408, 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=85.7MiB/s (89.9MB/s), 85.7MiB/s-85.7MiB/s (89.9MB/s-89.9MB/s), io=1024MiB (1074MB), run=11945-11945msec Disk stats (read/write): nvme0n1: ios=260906/3, merge=0/1, ticks=14618/4, in_queue=17670, util=100.00% Modified (with my patch): ---------------------------- 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): [R(1)][100.0%][r=74.1MiB/s,w=0KiB/s][r=18.0k,w=0 IOPS][eta 00m:00s] reader: (groupid=0, jobs=1): err= 0: pid=1808: Mon Nov 5 16:11:09 2018 read: IOPS=18.3k, BW=71.4MiB/s (74.9MB/s)(1024MiB/14334msec) slat (usec): min=18, max=4378, avg=52.59, stdev=63.66 clat (usec): min=31, max=15622, avg=3443.86, stdev=1431.27 lat (usec): min=81, max=15766, avg=3496.57, stdev=1450.21 clat percentiles (usec): | 1.00th=[ 2835], 5.00th=[ 2835], 10.00th=[ 2835], 20.00th=[ 2868], | 30.00th=[ 2868], 40.00th=[ 2868], 50.00th=[ 2868], 60.00th=[ 2900], | 70.00th=[ 2933], 80.00th=[ 3425], 90.00th=[ 5080], 95.00th=[ 6259], | 99.00th=[10159], 99.50th=[11076], 99.90th=[12649], 99.95th=[13435], | 99.99th=[14484] bw ( KiB/s): min=63142, max=77464, per=99.97%, avg=73128.46, stdev=3383.81, samples=28 iops : min=15785, max=19366, avg=18281.96, stdev=845.95, samples=28 lat (usec) : 50=0.01%, 100=0.01%, 250=0.01%, 500=0.01%, 750=0.01% lat (usec) : 1000=0.01% lat (msec) : 2=0.01%, 4=84.77%, 10=14.12%, 20=1.09% cpu : usr=2.20%, sys=95.72%, ctx=360, majf=0, minf=72 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=71.4MiB/s (74.9MB/s), 71.4MiB/s-71.4MiB/s (74.9MB/s-74.9MB/s), io=1024MiB (1074MB), run=14334-14334msec Disk stats (read/write): nvme0n1: ios=258235/3, merge=0/1, ticks=12583/10, in_queue=14779, util=100.00% thanks, -- John Hubbard NVIDIA
