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SubjectRe: RFC on io-stalls patch
On Tue, Jul 15 2003, Chris Mason wrote:
> On Tue, 2003-07-15 at 04:28, Jens Axboe wrote:
>
> > Definitely, because prepare to be a bit disappointed. Here are scores
> > that include 2.4.21 as well:
>
> > io_load:
> > Kernel [runs] Time CPU% Loads LCPU% Ratio
> > 2.4.21 3 543 49.7 100.4 19.0 4.08
> > 2.4.22-pre5 3 637 42.5 120.2 18.5 4.75
> > 2.4.22-pre5-axboe 3 540 50.0 103.0 18.1 4.06
>
> Huh, this is completely different than io_load on my box (2P scsi, ext3,
> data=writeback)
>
> io_load:
> Kernel [runs] Time CPU% Loads LCPU% Ratio
> 2.4.21 3 520 52.5 27.8 15.2 3.80
> 2.4.22-pre5 3 394 69.0 21.5 15.4 2.90
> 2.4.22-sync 3 321 84.7 16.2 15.8 2.36
>
> Where 2.4.22-sync was the variant I posted yesterday. I don't really
> see how 2.4.21 can get numbers as good as 2.4.22-pre5 on the io_load
> test, the read starvation with a big streaming io is horrible.
>
> The data=writeback is changing the workload significantly, I used it
> because I didn't want the data=ordered code to flush all dirty buffers
> every 5 seconds. I would expect ext3 data=ordered to be pretty
> starvation prone in 2.4.21 as well though.

Well maybe it's due to data=writeback? I'm using completely stock
options for ext3. You didn't mention tcq depth of your scsi drive, in my
experience it's worthless to test io scheduler behaviour using more than
a few tags.

> BTW, the contest run times vary pretty wildy. My 3 compiles with
> io_load running on 2.4.21 were 603s, 443s and 515s. This doesn't make
> the average of the 3 numbers invalid, but we need a more stable metric.

Mine are pretty consistent [1], I'd suspect that it isn't contest but your
drive tcq skewing things. But it would be nice to test with other things
as well, I just used contest because it was at hand.

[1] when the current run completes, I can post them all.

--
Jens Axboe

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