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SubjectRe: [PATCH] Add ext3 data=guarded mode
On (Fri) Apr 17 2009 [16:13:42], Theodore Tso wrote:
> On Fri, Apr 17, 2009 at 11:39:06PM +0530, Amit Shah wrote:
> > # 4GiB file, kernel 9f76208c33984ab777eace5d07a4e36e88703e02 + ext3-guarded
> >
> > filesystem posix-fallocate mmap chunk-4096 chunk-8192
> > ext3-guarded 85 97 459 90
> > ext3-writeback 86 95 140 94
> > ext3-ordered 86 96 277 95
> >
> > Running the test in single user mode, I get the following results:
> >
> > # 4GiB file, kernel 9f76208c33984ab777eace5d07a4e36e88703e02 + ext3-guarded
> >
> > filesystem posix-fallocate mmap chunk-4096 chunk-8192
> > ext3-guarded 84 86 163 91
> > ext3-writeback 84 88 217 91
> > ext3-ordered 84 86 226 91
>
>
> The difference between guarded and writeback in chunk-4096 looking at
> your desktop timings and your single user times is.... surprising.

Surely. I re-ran the guarded test immediately after that one and got a
time of 353s with the desktop. Another run much latergave me a 189s time,
so it seems to vary quite a lot. Initially when I was getting high
numbers, I thought it could be related to the IO scheduler but looks like
it's just some background tasks trying to get cpu or io time. Of course,
the whole system becomes sluggish once these tests start.

> In particular, the fact that the guarded time is 3 times longer than
> ext3-writeback when the desktop is running, and 20% faster in single
> user mode. Are these results reproducible? And do you have any
> thoughts as to what might be causing them?

I initially thought there was something but I also got lower numbers
(189s), so I can't really say what it is even though I call sync before
starting the tests.

Amit


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