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
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