HEVC plugin transcoding very slow

Hi, 

recently I've started experimenting with HEVC plugin, which provide software HEVC decoder and encoder implementations. I've install Professional edition, recompile kernel with included patchset, and run test:

~# /opt/intel/mediasdk/samples/_bin/x64/sample_multi_transcode -i::h265 /opt/intel/mediasdk/samples/_bin/content/test_stream.265 -o::h265 test_out.h265 -sw -pe 2fca99749fdb49aeb121a5b63ef568f7
Multi Transcoding Sample Version 8.2.25.982

plugin_loader.h :172 [INFO] Plugin was loaded from GUID: { 0x15, 0xdd, 0x93, 0x68, 0x25, 0xad, 0x47, 0x5e, 0xa3, 0x4e, 0x35, 0xf3, 0xf5, 0x42, 0x17, 0xa6 } (Intel (R) Media SDK plugin for HEVC DECODE)
plugin_loader.h :172 [INFO] Plugin was loaded from GUID: { 0x2f, 0xca, 0x99, 0x74, 0x9f, 0xdb, 0x49, 0xae, 0xb1, 0x21, 0xa5, 0xb6, 0x3e, 0xf5, 0x68, 0xf7 } (Intel (R) Media SDK plugin for HEVC ENCODE)
Pipeline surfaces number (DecPool): 12
MFX SOFTWARE Session 0 API ver 1.25 parameters: 
Input  video: HEVC
Output video: HEVC

Session 0 was NOT joined with other sessions

Transcoding started
..
Transcoding finished

Common transcoding time is 1.46311 sec
-------------------------------------------------------------------------------
*** session 0 PASSED (MFX_ERR_NONE) 1.46296 sec, 101 frames
-i::h265 /opt/intel/mediasdk/samples/_bin/content/test_stream.265 -o::h265 test_out.h265 -sw -pe 2fca99749fdb49aeb121a5b63ef568f7 

-------------------------------------------------------------------------------

The test PASSED
plugin_loader.h :198 [INFO] MFXBaseUSER_UnLoad(session=0x0x55fc454a0bc0), sts=0
plugin_loader.h :198 [INFO] MFXBaseUSER_UnLoad(session=0x0x55fc454a0bc0), sts=0

So everything looks fine, and I've started to transcode my own files. And first sample gives me dramatically poor results: transcoding speed was getting around 3-5 fps.

~# /opt/intel/mediasdk/samples/_bin/x64/sample_multi_transcode -sw -i::h265 in.h265 -o::h265 out.h265 -b 18000 -MaxKbps 20000 -n 100 -u veryfast
Multi Transcoding Sample Version 8.2.25.982

plugin_loader.h :172 [INFO] Plugin was loaded from GUID: { 0x15, 0xdd, 0x93, 0x68, 0x25, 0xad, 0x47, 0x5e, 0xa3, 0x4e, 0x35, 0xf3, 0xf5, 0x42, 0x17, 0xa6 } (Intel (R) Media SDK plugin for HEVC DECODE)
plugin_loader.h :172 [INFO] Plugin was loaded from GUID: { 0x2f, 0xca, 0x99, 0x74, 0x9f, 0xdb, 0x49, 0xae, 0xb1, 0x21, 0xa5, 0xb6, 0x3e, 0xf5, 0x68, 0xf7 } (Intel (R) Media SDK plugin for HEVC ENCODE)
Pipeline surfaces number (DecPool): 15
MFX SOFTWARE Session 0 API ver 1.25 parameters: 
Input  video: HEVC
Output video: HEVC

Session 0 was NOT joined with other sessions

Transcoding started
.
Transcoding finished

Common transcoding time is 19.0315 sec
-------------------------------------------------------------------------------
*** session 0 PASSED (MFX_ERR_NONE) 19.0313 sec, 100 frames
-sw -i::h265 in.h265 -o::h265 out.h265 -b 18000 -MaxKbps 20000 -n 100 -u veryfast 

-------------------------------------------------------------------------------

The test PASSED
plugin_loader.h :198 [INFO] MFXBaseUSER_UnLoad(session=0x0x55d8bc1d6b50), sts=0
plugin_loader.h :198 [INFO] MFXBaseUSER_UnLoad(session=0x0x55d8bc1d6b50), sts=0

I think I have some error with my setup, but could not figured out where. On same CPU libx265 gives me around 25-30 fps ultrafast 3840x2160 transcoding, and I expect to get at least close results from MediaSDK HEVC plugin.

The input file: https://yadi.sk/d/mUOCI9shJQI68Q

I've tried to convert size to 1920x1080, convert input HEVC to 8 bits, select 25 fps input files, forcibly select chroma mode, direct select GUID of plugin. Also notice that I use only software implementation, without HW acceleration and CPU without quicksync support, but as I understand it should be fine.

My system: ubuntu 16.04.5, kernel 4.4.111 with patchset, MediaSDK 2018R1 Professional Edition for Linux.

Could you please help?