IMFS throughput (was Re: Unlinking large files in IMFS)

[Joel Sherrill]

Andy Dachs wrote:
> 
> > > Out of interest these are the tentative figures I got with a modified version of the iozone benchmark on my eval board (MPC8260, I & D caches off, 40MHz system clock, 1Mbyte file):
> > >
> > > IOZONE performance measurements: 624152 bytes/second for writing the file 2330168 bytes/second for reading the file
> >
> > Is this with the default block size?  I would be curious to see the
> > impact of
> > increasing it. It should lower the relative overhead of scanning the
> > block lists.
> >
> 
> Yes, that was with IMFS_MEMFILE_BYTES_PER_BLOCK set to 128.  Changing it to 512 does pretty much double the write speed (see below).

Then we are likely bound by the speed of malloc and memcpy on write and
memcpy on read.
When writing and extending a file, you are doing a malloc per block.  
 
> Andy
> 
>         IOZONE: Performance Test of Sequential File I/O  --  V1.14 (1/23/92)
>                 By Bill Norcott
> 
>         Operating System: POSIX 1003.1-1988
> 
>         Send comments to:       norcott_bill at tandem.com
> 
>         IOZONE writes a 1 Megabyte sequential file consisting of
>         2048 records which are each 512 bytes in length.
>         It then reads the file.  It prints the bytes-per-second
>         rate at which the computer can read and write files.
> 
> Writing the 1 Megabyte file, 'iozone.tmp'...0.820000 seconds
> Reading the file...0.350000 seconds
> 
> IOZONE performance measurements:
>         1278751 bytes/second for writing the file
>         2995931 bytes/second for reading the file
> 
> The test completed too quickly to give a good result
> You will get a more precise measure of this machine's
> performance by re-running IOZONE using the command:
> 
>         iozone 17       (i.e., file size = 17 megabytes)
> 
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