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Re: [PATCH] xfs/013: allow non-write fsstress operations in background w

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [PATCH] xfs/013: allow non-write fsstress operations in background workload
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 18 Jun 2014 09:55:46 +1000
Cc: fstests@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1401820129-6543-1-git-send-email-bfoster@xxxxxxxxxx>
References: <1401820129-6543-1-git-send-email-bfoster@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Tue, Jun 03, 2014 at 02:28:49PM -0400, Brian Foster wrote:
> It has been reported that test xfs/013 probably uses more space than
> necessary, exhausting space if run against a several GB sized ramdisk.
> xfs/013 primarily creates, links and removes inodes. Most of the space
> consumption occurs via the background fsstress workload.
> 
> Remove the fsstress -w option that suppresses non-write operations. This
> slightly reduces the storage footprint while still providing a
> background workload for the test.
> 
> Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>

This change makes the runtime blow out on a ramdisk from 4s to over
ten minutes on my test machine. Non-ramdisk machines seem to be
completely unaffected.

I was going to say "no, bad change", but I noticed that my
spinning disk VMs weren't affected at all. Looking more closely,
xfs/013 is now pegging all 16 CPUs on the VM. The profile:

-  60.73%  [kernel]  [k] do_raw_spin_lock
   - do_raw_spin_lock
      - 99.98% _raw_spin_lock
         - 99.83% sync_inodes_sb
              sync_inodes_one_sb
              iterate_supers
              sys_sync
              tracesys
              sync
-  32.76%  [kernel]  [k] delay_tsc
   - delay_tsc
      - 98.43% __delay
           do_raw_spin_lock
         - _raw_spin_lock
            - 99.99% sync_inodes_sb
                 sync_inodes_one_sb
                 iterate_supers
                 sys_sync
                 tracesys
                 sync

OK, that's a kernel problem, not a problem with the change in the
test...

/me goes and dusts off his "concurrent sync scalability" patches.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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