Messages in this thread | | | From | "Stephen C. Tweedie" <> | Date | Thu, 29 Jul 1999 05:01:31 +0100 (BST) | Subject | Re: (disk/cpu) kernel performance problem |
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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
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