On 09/11/2021 18:21, Kees Cook wrote:

On Fri, Nov 05, 2021 at 02:41:59PM +0800, kernel test robot wrote:

quoted

Greeting,

FYI, we noticed a -11.6% regression of netperf.Throughput_tps due to commit:


commit: a0918006f9284b77397ae4f163f055c3e0f987b2 ("[PATCH v15 1/3] fs: Add trusted_for(2) syscall implementation and related sysctl")
url: https://github.com/0day-ci/linux/commits/Micka-l-Sala-n/Add-trusted_for-2-was-O_MAYEXEC/20211013-032533
patch link: https://lore.kernel.org/kernel-hardening/20211012192410.2356090-2-mic@digikod.net (local)

in testcase: netperf
on test machine: 192 threads 4 sockets Intel(R) Xeon(R) Platinum 9242 CPU @ 2.30GHz with 192G memory
with following parameters:

	ip: ipv4
	runtime: 300s
	nr_threads: 16
	cluster: cs-localhost
	test: TCP_CRR
	cpufreq_governor: performance
	ucode: 0x5003006

test-description: Netperf is a benchmark that can be use to measure various aspect of networking performance.
test-url: http://www.netperf.org/netperf/


please be noted we made out some further analysis/tests, as Fengwei mentioned:
==============================================================================
Here is my investigation result of this regression:

If I add patch to make sure the kernel function address and data address is
almost same even with this patch, there is almost no performance delta(0.1%)
w/o the patch.

And if I only make sure function address same w/o the patch, the performance
delta is about 5.1%.

So suppose this regression is triggered by different function and data address.
We don't know why the different address could bring such kind of regression yet
===============================================================================


we also tested on other platforms.
on a Cooper Lake (Intel(R) Xeon(R) Gold 5318H CPU @ 2.50GHz with 128G memory),
we also observed regression but the gap is smaller:
=========================================================================================
cluster/compiler/cpufreq_governor/ip/kconfig/nr_threads/rootfs/runtime/tbox_group/test/testcase/ucode:
  cs-localhost/gcc-9/performance/ipv4/x86_64-rhel-8.3/16/debian-10.4-x86_64-20200603.cgz/300s/lkp-cpl-4sp1/TCP_CRR/netperf/0x700001e

commit:
  v5.15-rc4
  a0918006f9284b77397ae4f163f055c3e0f987b2

       v5.15-rc4 a0918006f9284b77397ae4f163f
---------------- ---------------------------
         %stddev     %change         %stddev
             \          |                \
    333492            -5.7%     314346 ±  2%  netperf.Throughput_total_tps
     20843            -4.5%      19896        netperf.Throughput_tps


but no regression on a 96 threads 2 sockets Ice Lake with 256G memory:
=========================================================================================
cluster/compiler/cpufreq_governor/ip/kconfig/nr_threads/rootfs/runtime/tbox_group/test/testcase/ucode:
  cs-localhost/gcc-9/performance/ipv4/x86_64-rhel-8.3/16/debian-10.4-x86_64-20200603.cgz/300s/lkp-icl-2sp1/TCP_CRR/netperf/0xb000280

commit:
  v5.15-rc4
  a0918006f9284b77397ae4f163f055c3e0f987b2

       v5.15-rc4 a0918006f9284b77397ae4f163f
---------------- ---------------------------
         %stddev     %change         %stddev
             \          |                \
    555600            -0.1%     555305        netperf.Throughput_total_tps
     34725            -0.1%      34706        netperf.Throughput_tps


Fengwei also helped review these results and commented:
I suppose these three CPUs have different cache policy. It also could be
related with netperf throughput testing.

Does moving the syscall implementation somewhere else change things?
That's a _huge_ performance change for something that isn't even called.
What's going on here?

This regression doesn't make sense. I guess this is the result of a
flaky netperf test, maybe because the test machine was overloaded at
that time.