Re: How to speed up stream & record handling?

[nickroberts@ukf.net (Nick Roberts)]

On 21 Feb 2002 04:37:57 -0800, karlran1234@yahoo.com (Karl Ran) strongly
typed:

>Hello,
>I've a problem getting a reasonable IO preformance from an Ada
>program (source is attached)
>
>The environment looks like this:
>OS: linux-2.4.16
>CPU: Intel P3/700 MHz / BX chipset
>compiler: gnat-3.14p
>
>The program reads a packet of data (200 bytes) and converts the
>header(2 bytes) to match the architecture.  It will do it 100000 times.
>...

My suggestion (you may not like it!) is: (a) if possible, ensure the
NIC/DMA dumps the data into a useful piece of memory (i.e. shared); (b)
preferably, use assembly.

>It's too slow for the target application.

Which is, please?

>I know the the PC achitecture is known for their bad IO performance,
>but this 2.4 MBytes/s seems not be related to the PC-IO-bottleneck...  

I'm sorry but this is a jaw-dropper. Speak not of that which thou wot not
of, child.

My suggestion for improvements in your Ada code follows.

with Ada.Text_IO;
with Ada.Streams.Stream_IO;

procedure Slow_Ada is

	type Machine_Architecture is (Little_Endian, Big_Endian);

	Architecture: constant Machine_Architecture := Little_Endian; -- IA

   subtype Must_Be_True is Boolean range True..True;

   Check_Element_Size: constant Must_Be_True := 
									Ada.Streams.Stream_Element'Size = 8;

   subtype Data_Array is Ada.Streams.Stream_Element_Array(1..200);

   procedure Adjust_Data (Data: in out Data_Array) is

		Temp: Ada.Streams.Stream_Element; -- assuming this is a byte

   begin
		case Architecture is
			when Little_Endian =>
				Temp      := Data(199); 
				Data(199) := Data(200);
				Data(200) := Temp;
			when Big_Endian =>
				null;
      end case;
   end Adjust_Data;

	pragma Inline(Adjust_Data);

   Item: Data_Array;
   Last: Ada.Streams.Stream_Element_Offset;
   File: Ada.Streams.Stream_IO.File_Type;

begin

   Ada.Streams.Stream_IO.Open
     (Name => "/dev/zero", --use any big file you like (20 MByte)
      File => File,
      Mode => Ada.Streams.Stream_IO.In_File);

   Put("Starting...");

   for I in 1 .. 100000 loop
		--- test for end of file?
		Read(File,Item,Last);
      -- test Last for /= 200?
      Adjust_Data(Item);
		-- do something with the data?
   end loop;

	Put_Line("Done.");

   Ada.Streams.Stream_IO.Close (File);

end Slow_Ada;

If a stream element isn't a byte, you'll need to adjust Adjust_Data (and
remove or change Check_Element_Size). At this (low) level, this sort of
twiddling will always be necessary.

(Also, note how my code does the job with the minimum of 'fuss'.)

Hope this helps.

-- 
Nick Roberts