Hello Everybody,

I am not sure where I should post this question so I try it here first.

On my KVM VPS, I am trying to get the UnixBench score of kernel 4.1.5 to
the same level as the one of Devuan kernel 3.16.7-ckt11-1+deb8u3. The
issue is mainly on the performance of running parallel processes. The
scores for single process are quite similar. The setup is exactly the
same, so I just boot using each kernel and run UnixBench. But the
results are quite different as you can see at the bottom of this email.

One thing that I am not sure of is the use of virtio-pci driver. When I
boot my KVM VPS using Devuan kernel 3.16.7-ckt11-1+deb8u3, I got the
following on dmesg:

virtio-pci 0000:00:03.0: irq 40 for MSI/MSI-X
virtio-pci 0000:00:03.0: irq 41 for MSI/MSI-X
virtio-pci 0000:00:03.0: irq 42 for MSI/MSI-X
virtio-pci 0000:00:04.0: irq 43 for MSI/MSI-X
virtio-pci 0000:00:04.0: irq 44 for MSI/MSI-X

On kernel 4.1.15, I got the following:

virtio-pci 0000:00:03.0: virtio_pci: leaving for legacy driver
virtio-pci 0000:00:04.0: virtio_pci: leaving for legacy driver
virtio-pci 0000:00:05.0: virtio_pci: leaving for legacy driver

I have got the kernel config of 4.1.15 based on the one of 3.16.7. I
just did "make oldconfig" and took the default values for the new entries.

When I disabled CONFIG_VIRTIO_PCI_LEGACY on kernel 4.1.15, my VPS failed
to boot and dropped into initramfs prompt. There is no
CONFIG_VIRTIO_PCI_LEGACY on kernel 3.16.7.

I have got the impression that kernel 3.16.7 does not use legacy driver.
Is that true or is that just the illusion of the dmesg display so that
kernel 3.16.7 actually uses legacy driver?

Do you have any suggestions on where to look at to improve the
performance of kernel 4.1.15?

Thanks in advance for your help.

Kind regards,

Anto
----

OS: GNU/Linux -- 3.16.0-4-amd64 -- #1 SMP Debian 3.16.7-ckt11-1+deb8u3
(2015-08-04)
------------------------------------------------------------------------
Benchmark Run: Sat Jan 23 2016 16:17:26 - 16:45:46
2 CPUs in system; running 2 parallel copies of tests

Dhrystone 2 using register variables       50659090.7 lps   (10.0 s, 7 
samples)
Double-Precision Whetstone                     7125.6 MWIPS (10.0 s, 7 
samples)
Execl Throughput                               6829.9 lps   (29.9 s, 2 
samples)
File Copy 1024 bufsize 2000 maxblocks       1164709.8 KBps  (30.0 s, 2 
samples)
File Copy 256 bufsize 500 maxblocks          369515.8 KBps  (30.0 s, 2 
samples)
File Copy 4096 bufsize 8000 maxblocks       2681384.0 KBps  (30.0 s, 2 
samples)
Pipe Throughput                             3296092.2 lps   (10.0 s, 7 
samples)
Pipe-based Context Switching                 614170.0 lps   (10.0 s, 7 
samples)
Process Creation                              13784.1 lps   (30.0 s, 2 
samples)
Shell Scripts (1 concurrent)                   9228.9 lpm   (60.0 s, 2 
samples)
Shell Scripts (8 concurrent)                   1468.9 lpm   (60.0 s, 2 
samples)
System Call Overhead                        4345996.5 lps   (10.0 s, 7 
samples)

System Benchmarks Index Values               BASELINE RESULT    INDEX
Dhrystone 2 using register variables         116700.0 50659090.7   4341.0
Double-Precision Whetstone                       55.0 7125.6   1295.6
Execl Throughput                                 43.0 6829.9   1588.4
File Copy 1024 bufsize 2000 maxblocks          3960.0 1164709.8   2941.2
File Copy 256 bufsize 500 maxblocks            1655.0 369515.8   2232.7
File Copy 4096 bufsize 8000 maxblocks          5800.0 2681384.0   4623.1
Pipe Throughput                               12440.0 3296092.2   2649.6
Pipe-based Context Switching                   4000.0 614170.0   1535.4
Process Creation                                126.0 13784.1   1094.0
Shell Scripts (1 concurrent)                     42.4 9228.9   2176.6
Shell Scripts (8 concurrent)                      6.0 1468.9   2448.1
System Call Overhead                          15000.0 4345996.5   2897.3
========
System Benchmarks Index Score                                        2269.1

OS: GNU/Linux -- 4.1.15-kvm-v3 -- #1 SMP Sat Jan 23 15:34:21 CET 2016
------------------------------------------------------------------------
Benchmark Run: Sat Jan 23 2016 17:45:23 - 18:14:43
2 CPUs in system; running 2 parallel copies of tests

Dhrystone 2 using register variables       33186817.4 lps   (10.0 s, 7 
samples)
Double-Precision Whetstone                     6982.4 MWIPS (9.7 s, 7 
samples)
Execl Throughput                               4174.1 lps   (29.7 s, 2 
samples)
File Copy 1024 bufsize 2000 maxblocks        874549.1 KBps  (30.0 s, 2 
samples)
File Copy 256 bufsize 500 maxblocks          269488.6 KBps  (30.0 s, 2 
samples)
File Copy 4096 bufsize 8000 maxblocks       1738899.1 KBps  (30.0 s, 2 
samples)
Pipe Throughput                             2204174.7 lps   (10.0 s, 7 
samples)
Pipe-based Context Switching                 282724.3 lps   (10.0 s, 7 
samples)
Process Creation                               8668.9 lps   (30.0 s, 2 
samples)
Shell Scripts (1 concurrent)                   6661.8 lpm   (60.0 s, 2 
samples)
Shell Scripts (8 concurrent)                   1067.7 lpm   (60.1 s, 2 
samples)
System Call Overhead                        3376500.3 lps   (10.0 s, 7 
samples)

System Benchmarks Index Values               BASELINE RESULT    INDEX
Dhrystone 2 using register variables         116700.0 33186817.4   2843.8
Double-Precision Whetstone                       55.0 6982.4   1269.5
Execl Throughput                                 43.0 4174.1    970.7
File Copy 1024 bufsize 2000 maxblocks          3960.0 874549.1   2208.5
File Copy 256 bufsize 500 maxblocks            1655.0 269488.6   1628.3
File Copy 4096 bufsize 8000 maxblocks          5800.0 1738899.1   2998.1
Pipe Throughput                               12440.0 2204174.7   1771.8
Pipe-based Context Switching                   4000.0 282724.3    706.8
Process Creation                                126.0 8668.9    688.0
Shell Scripts (1 concurrent)                     42.4 6661.8   1571.2
Shell Scripts (8 concurrent)                      6.0 1067.7   1779.5
System Call Overhead                          15000.0 3376500.3   2251.0
========
System Benchmarks Index Score                                        1558.2