lkml.org 
[lkml]   [1999]   [Jul]   [29]   [last100]   RSS Feed
Views: [more markup]  [less markup]  [headers]  [forward] 
 
Messages in this thread
/
From"Stephen C. Tweedie" <>
DateThu, 29 Jul 1999 05:01:31 +0100 (BST)
SubjectRe: (disk/cpu) kernel performance problem
Hi,

On Wed, 28 Jul 1999 16:12:59 -0700 (PDT), Gerald Aigner
<aigner@stanford.edu> said:

> I just profiled the 2.3.11 kernel and around 37% of the time was spend in
> file_read_actor. By looking at the function I discovered that this
> function is responsible for copying data from the kernel to the user
> space.

> Here the basic performance of this function: 
>   data transfered:                      1.8 GB
>   total execution time of the function:  23 seconds
>   ---------------------------------------------------
>   throughput per second:                 78 MB/sec

> This means that the Linux memory copy function used for copying 
> disk data achieves a memory bandwidth of approximately 156 MB/sec 
> on a system with a 66 MHz system bus. 

Remember that you are doing disk IO here too so there is also 78MB/sec
of bus traffic going between the scsi controller and main memory.
That's also going to reduce the available bandwidth.  Try doing a copy
purely out of cache to see what the real memory bandwidth available via
the filesystem is.

--Stephen

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:53    [from the cache]
©2003-2008