[SPDK] Re: Performance of spdk_trace

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Hi Jinhao,

I=E2=80=99m not aware of any detailed benchmarking, but it can certainly su=
pport the trace event rates that you describe.

You can use the null bdev w/ the bdevperf application as a rough approximat=
ion.  Each bdev IO generates two trace events (one for IO start, one for IO=
 end), so we can use the null bdev as an easy test to generate as many of t=
hose trace events as possible.

First put the following in a file named null.json:

{
  "subsystems": [
    {
      "subsystem": "bdev",
      "config": [
        {
          "method": "bdev_null_create",
          "params": {
            "name": "null0",
            "num_blocks": 2097152,
            "block_size": 512
          }
        }
      ]
    }
  ]
}

Then run the bdevperf app without events:

test/bdev/bdevperf/bdevperf -q 4 -o 1024 -w randread -t 5 -c null.json

In one of my development VMs, I see 20M IO/s.  This is roughly 50ns per IO.

Next run it with bdev trace events enabled by adding the =E2=80=9C-e bdev=
=E2=80=9D command line option:

test/bdev/bdevperf/bdevperf -q 4 -o 1024 -w randread -t 5 -c null.json -e b=
dev

In the same VM, I see 14M IO/s.  This is roughly 70ns per IO.  That=E2=80=
=99s 20ns extra overhead for 2 trace events.

It scales to multiple cores as well =E2=80=93 add =E2=80=9C-m 0xF -C=E2=80=
=9D to both bdevperf command lines and it will do the same test on 4 cores =
at once with roughly that same 20M v. 14M IO/s on each of the 4 cores.

Of course your platform will have different hardware, so results will vary =
somewhat.  The rate limit will also depend on the number and size of the tr=
ace arguments for each trace event.

Best regards,

Jim Harris




From: Jinhao Fan <fanjinhao21s(a)ict.ac.cn>
Date: Sunday, August 28, 2022 at 6:14 PM
To: spdk(a)lists.01.org <spdk(a)lists.01.org>
Subject: [SPDK] Performance of spdk_trace
Hi there,

During my daily use I found the tracing system of SPDK and spdk_trace_record
very low overhead. So I=E2=80=99m planning to port to other applications wh=
ere it
might generate several 100K events per second. I think such a speed should
be normal for SPDK applications. Have you ever measured how many events per
second is spdk_trace able to handle?

Thanks!

Jinhao Fan
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