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SubjectRe: [PATCH] Add ext3 data=guarded mode
On (Sat) Apr 18 2009 [09:28:21], Mike Galbraith wrote:
> On Sat, 2009-04-18 at 11:33 +0530, Amit Shah wrote:
> > 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.
>
> Probably because you're swapping heavily, and that is perturbing your

The variance only affects the 4k test; the other times more or less
remain the same.

Amit


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