Sometime ago, there was a brief mention of multi-threading FPC would be counter productive because compilation process was mostly disk IO bound --this is what I understood anyway.
I wanted to check to see if disk IO was really limiting FPC/Lazarus compile performance.
The only quick way I could devise to check this was to use two different disks which are significantly different from one another in terms of performance.
And, to help with timing, I modified the mnuToolBuildLazarusClicked() event (in \lazarus\ide\main.pp). [See below for code.]
Here is test setup:
OS: Win7, x64, 8 GB RAM.
Disk1: SSD, OCZ Vertex, NTFS
Disk2: RAMDisk, Dataram, NTFS [
http://memory.dataram.com/products-and-services/software/ramdisk ]
To show that these disks perform significantly differently from one another, I used 'ATTO Disk Benchmark' (default settings) and took the max values for each disk.
SSD: Read: 200 MB/s Write: 198 MB/s
RAMDisk: Read: 2,227 MB/s Write: 1,545 MB/s
IOW, RAMDisk is between 8 and 11 times faster than the SSD --significant enough for my purposes.
I used this version of Lazarus: lazarus-0.9.28.2-fpc-2.2.4-win64.exe
Identical copies of (default setup of) Lazarus on both disks. Nothing, other than the relevant paths altered by me.
Testing:
Rebuild Lazarus 10 times on each disk. Here are the values:
SSD:
01: 105,498 ms
02: 103,678 ms
03: 103,345 ms
04: 101,522 ms
05: 104,720 ms
06: 101,874 ms
07: 100,136 ms
08: 100,492 ms
09: 104,850 ms
10: 104,488 ms
RAMDisk:
01: 101,150 ms
02: 111,198 ms
03: 109,066 ms
04: 103,516 ms
05: 105,875 ms
06: 103,133 ms
07: 104,036 ms
08: 108,763 ms
09: 104,306 ms
10: 103,583 ms
Here are the average values:
SSD: 103,060 ms (1 min 43 sec)
RAMDisk: 105,463 ms (1 min 46 sec)
This doesn't make sense. FPC/Lazarus compiles on the faster medium longer (albeit only 3 sec.).
But, more than that, I can't see how FPC/Lazarus would be disk IO bound, if it takes practically the same time on a medium that is 8-11 times faster than the other one.
While doing the builds, I kept an eye on the other parameters too. This is an 8-core machine, and never during this test did any core hit anything beyond %20. Same with paging.. It practically stayed the same.
If it isn't disk IO, if it isn't CPU load; then what is it?
RAM IO bound?
Could it be?
-------------------------------------------------------------- here is modified code:
--------------------------------------------------------------
procedure TMainIDE.mnuToolBuildLazarusClicked(Sender: TObject);
var
StartTime1: TDateTime;
EndTime1: TDateTime;
Path1: String;
Times1: TStringList;
DoTime1: Boolean;
MilliSecs1: Int64;
begin
if MiscellaneousOptions.BuildLazOpts.ConfirmBuild then
if MessageDlg(lisConfirmLazarusRebuild, mtConfirmation, mbYesNo,
0)mrYes then exit;
DoTime1 := MessageDlg('Do you also want to time the build process',
mtConfirmation, mbYesNo, 0) = mrYes;
if DoTime1 then begin
Times1:= TStringList.Create;
StartTime1 := Now();
end;
try
DoBuildLazarus([]);
finally
if DoTime1 then begin
EndTime1 := Now();
Path1 :=
IncludeTrailingPathDelimiter(ExtractFilePath(Application.ExeName)) +
'BuildTime.txt';
MilliSecs1 := MilliSecondsBetween(StartTime1, EndTime1);
if FileExists(Path1) then Times1.LoadFromFile(Path1);
Times1.Add(IntToStr(MilliSecs1));
Times1.SaveToFile(Path1);
Times1.Free;
end;
end;
end;