Messages in this thread | | | Date | Mon, 26 Jul 1999 19:33:23 -0700 (PDT) | From | Gerald Aigner <> | Subject | Re: (disk/cpu) 2.3.11 kernel performance problem |
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On Mon, 26 Jul 1999, Rik van Riel wrote:
> On Mon, 26 Jul 1999, Gerald Aigner wrote: > > > While optimizing the program I discovered that disk I/O > > performance in Linux could be improved substantially. In > > particular, there are two main problems: > > > > 1) The kernel copies data many times before it ends up in user > > space. > > > I'm very sorry, but you seem to be too late. This problem is > (at least partially) fixed in the newer 2.3 kernels... >
I just tried the 2.3.11 kernel. The new kernel is slightly faster (67 seconds instead of 69 seconds) and it uses less CPU time (37% vs. 45%)
However 37% is still a very high CPU utilization.
> > 2) Using mmap doesn't help because it serializes I/O within a single > > process (you can't read simultaneously from two disks). > > A single process uses a single thread of control, and yes, > we do readahead over RAID0 sets... >
Using mmap on the linux2.3.11 kernel takes now 105 seconds, which is still slower than doing read system calls in separate threads.
However overall CPU utilization is lower (around 7%) using mmap.
So is there an easy way to make mmap as fast as read (in terms of wall clock time).
-Gerald
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