Sorry to be obnoxious, but why is an app doing 1 byte reads the
filesystem's problem? This seems like something that really should
be the responsibility of the application, not the FS.
why isn't the java runtime doing some read-ahead of it's own?
On Tue, Jul 17, 2007 at 07:26:26PM +0800, Stuart Midgley wrote:
> Extra, I zero'ed /proc/fs/lustre/llite/fs0/read_ahead_stats and re-
> ran the test and checked the read ahead stats afterward... and they
> were all zero. So, I assume this means that Lustre isn't doing any
> read ahead in this case.
>
>
> On 17/07/2007, at 9:49 AM, Stuart Midgley wrote:
>
> >We are seeing really bad performance from a java app and it boils
> >down to
> >poor performance from 1-byte reads from a Lustre file system. After a
> >detailed strace of the application running, I have generated the
> >following
> >code snippet which demonstrates the problem
> >
> >#include <sys/stat.h>
> >#include <fcntl.h>
> >#include <unistd.h>
> >
> >int main(int argc, char **argv) {
> > int fd=open("5GB_file", O_RDONLY, 0666);
> > int i,j;
> > char b[1];
> >
> > for(i=0; i<10000; i++) {
> > lseek(fd, i*500, SEEK_SET);
> > for(j=0; j<100; j++) {
> > read(fd, b, 1);
> > }
> > }
> > close(fd);
> >}
> >
> >
> >5GB_file is just a dd if=/dev/zero of=5GB_file bs=1024k count=5000 .
> >
> >Anyway, this code runs in <1s on local disk, ~5s on NFS and >30s on
> >Lustre... I was disappointed to see Lustre slower than nfs. I was
> >hoping that Lustre's read-a-head would have been triggered by this
> >code,
> >but it doesn't appear to be. Any way I can tune Lustre to work better
> >with this code? (I know, change the code, but it isn't that easy -
> >this
> >is a c example of an strace of a java app - and changing the
> >original java
> >app isn't so easy).
> >
> >Thanks
> >Stu.
> >
>
>
> --
> Dr Stuart Midgley
> [EMAIL PROTECTED]
>
>
>
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--
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Troy Benjegerdes 'da hozer' [EMAIL PROTECTED]
Somone asked me why I work on this free (http://www.fsf.org/philosophy/)
software stuff and not get a real job. Charles Shultz had the best answer:
"Why do musicians compose symphonies and poets write poems? They do it
because life wouldn't have any meaning for them if they didn't. That's why
I draw cartoons. It's my life." -- Charles Shultz
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