makedumpfile mmap() benchmark

[Cliff Wickman]

> Jingbai Ma wote on 27 Mar 2013:
> I have tested the makedumpfile mmap patch on a machine with 2TB memory, 
> here is testing results:
> Test environment:
> Machine: HP ProLiant DL980 G7 with 2TB RAM.
> CPU: Intel(R) Xeon(R) CPU E7- 2860  @ 2.27GHz (8 sockets, 10 cores)
> (Only 1 cpu was enabled the 2nd kernel)
> Kernel: 3.9.0-rc3+ with mmap kernel patch v3
> vmcore size: 2.0TB
> Dump file size: 3.6GB
> makedumpfile mmap branch with parameters: -c --message-level 23 -d 31 
> --map-size <map-size>
> All measured time from debug message of makedumpfile.
> 
> As a comparison, I also have tested with original kernel and original 
> makedumpfile 1.5.1 and 1.5.3.
> I added all [Excluding unnecessary pages] and [Excluding free pages] 
> time together as "Filter Pages", and [Copyying Data] as "Copy data" here.
> 
> makedumjpfile	Kernel	map-size (KB)	Filter pages (s)	Copy data (s)	Total (s)
> 1.5.1	 3.7.0-0.36.el7.x86_64	N/A	940.28	1269.25	2209.53
> 1.5.3	 3.7.0-0.36.el7.x86_64	N/A	380.09	992.77	1372.86
> 1.5.3	v3.9-rc3	N/A	197.77	892.27	1090.04
> 1.5.3+mmap	v3.9-rc3+mmap	0	164.87	606.06	770.93
> 1.5.3+mmap	v3.9-rc3+mmap	4	88.62	576.07	664.69
> 1.5.3+mmap	v3.9-rc3+mmap	1024	83.66	477.23	560.89
> 1.5.3+mmap	v3.9-rc3+mmap	2048	83.44	477.21	560.65
> 1.5.3+mmap	v3.9-rc3+mmap	10240	83.84	476.56	560.4

I have also tested the makedumpfile mmap patch on a machine with 2TB memory, 
here are the results:
Test environment:
Machine: SGI UV1000 with 2TB RAM.
CPU: Intel(R) Xeon(R) CPU E7- 8837  @ 2.67GHz
(only 1 cpu was enabled in the 2nd kernel)
Kernel: 3.0.13 with mmap kernel patch v3 (I had to tweak the patch a bit)
vmcore size: 2.0TB
Dump file size: 3.6GB
makedumpfile mmap branch with parameters: -c --message-level 23 -d 31 
   --map-size <map-size>
All measured times are actual clock times.
All tests are noncyclic.   Crash kernel memory: crashkernel=512M

As did Jingbai Ma, I also tested with an unpatched kernel and
makedumpfile 1.5.1 and 1.5.3.  But they do 2 filtering scans: unnecessary
pages and free pages; here added together as filter pages time.

                                      Filter    Copy
makedumpfile Kernel	 map-size(KB) pages(s)	data(s) Total(s)
1.5.1	     3.0.13	   N/A	      671   	511    1182
1.5.3	     3.0.13	   N/A	      294       535     829
1.5.3+mmap   3.0.13+mmap     0	       54    	506   	560
1.5.3+mmap   3.0.13+mmap  4096	       40    	416	456
1.5.3+mmap   3.0.13+mmap 10240	       37	424	461

Using mmap for the copy data as well as for filtering pages did little:
1.5.3+mmap   3.0.13+mmap  4096	       37    	414	451

My results are quite similar to Jingbai Ma's.
The mmap patch to the kernel greatly speeds the filtering of pages, so
we at SGI would very much like to see this patch in the 3.10 kernel.
  http://marc.info/?l=linux-kernel&m=136627770125345&w=2

What puzzles me is that the patch greatly speeds the read's of /proc/vmcore
(where map-size is 0) as well as providing the mmap ability.  I can now
seek/read page structures almost as fast as mmap'ing and copying them.
(versus Jingbai Ma's results where mmap almost doubled the speed of reads)
I have put counters in to verify, and we are doing several million
seek/read's vs. a few thousand mmap's.  Yet the performance is similar
(54sec vs. 37sec, above). I can't rationalize that much improvement.

Thanks,
Cliff Wickman