Re: [RFC][PATCH 0/6] per device dirty throttling

On Tue, 2007-03-20 at 20:38 +1100, David Chinner wrote:
On Tue, Mar 20, 2007 at 09:08:24AM +0100, Peter Zijlstra wrote:
On Tue, 2007-03-20 at 18:47 +1100, David Chinner wrote:
So overall we've lost about 15-20% of the theoretical aggregate
perfomrance, but we haven't starved any of the devices over a
long period of time.

However, looking at vmstat for total throughput, there are periods
of time where it appears that the fastest disk goes idle. That is,
we drop from an aggregate of about 550MB/s to below 300MB/s for
several seconds at a time. You can sort of see this from the file
size output above - long term the ratios remain the same, but in the
short term we see quite a bit of variability.

I suspect you did not apply 7/6? There is some trouble with signed vs
unsigned in the initial patch set that I tried to 'fix' by masking out
the MSB, but that doesn't work and results in 'time' getting stuck for
about half the time.

I applied the fixes patch as well, so i had all that you posted...

Humm, not that then.

but it's almost
like it is throttling a device completely while it allows another
to finish writing it's quota (underestimating bandwidth?).

Yeah, there is some lumpy-ness in BIO submission or write completions it
seems, and when that granularity (multiplied by the number of active
devices) is larger than the 'time' period over with we average
(indicated by vm_cycle_shift) very weird stuff can happen.

Sounds like the period is a bit too short atm if we can get into this
sort of problem with only 2 active devices....

Yeah, trouble is, I significantly extended this period in 7/6.
Will have to ponder a bit on what is happening then.

Anyway, thanks for the feedback.

I'll try and reproduce the umount problem, maybe that will give some
hints.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

Relevant Pages

  • Re: Great SWT Program
    ... Yeah, yeah, just ... ways to get the same effect with more trouble. ... you can navigate with LESS trouble using the conveniently ... supplied direction keys that all modern keyboards have" thing. ...
    (comp.lang.java.programmer)
  • Re: 2nd Season Chuck - Cougars - 5 star poll - SPOILERS AHOY !
    ... I must admit that I had some trouble with "I saved your father's ... life by putting him in prison where any of the angry people he ... that was "do the writers think we're that stupid or does tony todd ... I was thinking Bones, but yeah. ...
    (rec.arts.tv)
  • Re: One thing I noticed
    ... >> A lot of guys who were too young to remember have that same trouble, ... >> yeah. ... Windows, from this perspective, ... out of facing their own self-imposed reality. ...
    (microsoft.public.vb.general.discussion)
  • Re: Javon Walker out for year
    ... >> Reported on Packers post-game show. ... > Yeah, I'm in trouble, I didn't draft a WR till the 4 th round, and it ...
    (rec.sport.football.fantasy)
  • Re: Potting Vandas
    ... Yeah, I have trouble with them too. ... (the Vascostylises) ... air-layering tehnique and see if this works. ...
    (rec.gardens.orchids)