[Cluster-devel] [GFS2 PATCH] GFS2: Average in only non-zero round-trip times for congestion stats

[Steven Whitehouse <swhiteho@redhat.com>]

Hi,

On 23/04/15 17:45, Bob Peterson wrote:
> ----- Original Message -----
>> Hi,
>>
>> That looks better. Do you get better results with it compared with the
>> previous version?
>>
>> Steve.
>>
>> On 22/04/15 18:00, Bob Peterson wrote:
>>> Hi,
>>>
>>> This patch changes function gfs2_rgrp_congested so that it only factors
>>> in non-zero values into its average round trip time. If the round-trip
>>> time is zero for a particular cpu, that cpu has obviously never dealt
>>> with bouncing the resource group in question, so factoring in a zero
>>> value will only skew the numbers. It also fixes a compile error on
>>> some arches related to division.
>>>
>>> Regards,
>>>
>>> Bob Peterson
>>> Signed-off-by: Bob Peterson <rpeterso@redhat.com>
> It's not straightforward because the "preferred rgrps" patch skews the
> performance results greatly. However, based on my performance tests, yes,
> the numbers do look better. I temporarily commented out that "preferred
> rgrps" patch to get a clearer picture. Here are numbers from my testing:
> This test consists of 5 nodes all simultaneously doing this 'dd' command:
> dd if=/dev/zero of=/mnt/gfs2/`hostname` bs=1M count=100
> (after drop_caches)
>
> Stock (nothing disabled):
>              Run 1
>           --------
> pats     716 MB/s
> jets     615 MB/s
> bills    669 MB/s
> dolphins 605 MB/s
> ravens   735 MB/s
>           --------
> Average: 668 MB/s
>
> Stock (plus preferred rgrps disabled): AKA 'c3'
>              Run 1     Run 2
>           --------  --------
> pats     766 MB/s  675 MB/s
> jets     649 MB/s  716 MB/s
> bills    790 MB/s  735 MB/s
> dolphins 761 MB/s  727 MB/s
> ravens   712 MB/s  728 MB/s
>           --------  --------
> Average: 736 MB/s  716 MB/s
>
> Without latest patch (plus preferred rgrps disabled): AKA 'c2'
> (In other words, this is the previous patch which was called
> "GFS2: Use average srttb value in congestion calculations")
>              Run 1     Run 2     Run 3
>           --------  --------  ---------
> pats     830 MB/s  688 MB/s  697 MB/s
> jets     833 MB/s  622 MB/s  645 MB/s
> bills    831 MB/s  796 MB/s  637 MB/s
> dolphins 834 MB/s  597 MB/s  690 MB/s
> ravens   815 MB/s  731 MB/s  734 MB/s
>           --------  --------  ---------
> Average: 829 MB/s  687 MB/s  681 MB/s
>
> Latest patch (plus preferred rgrps disabled):
>              Run 1     Run 2     Run 3
>           --------  --------  ---------
> pats     811 MB/s  829 MB/s  652 MB/s
> jets     825 MB/s  863 MB/s  702 MB/s
> bills    846 MB/s  825 MB/s  710 MB/s
> dolphins 845 MB/s  845 MB/s  683 MB/s
> ravens   820 MB/s  818 MB/s  682 MB/s
>           --------  --------  ---------
> Average: 829 MB/s  836 MB/s  686 MB/s
>
> Latest patch (nothing disabled):
>              Run 1     Run 2     Run 3
>           --------  --------  ---------
> pats     834 MB/s  817 MB/s  819 MB/s
> jets     837 MB/s  835 MB/s  836 MB/s
> bills    841 MB/s  837 MB/s  834 MB/s
> dolphins 838 MB/s  851 MB/s  842 MB/s
> ravens   795 MB/s  808 MB/s  815 MB/s
>           --------  --------  ---------
> Average: 829 MB/s  830 MB/s  829 MB/s
>
> This test (simultaneous dd) is known to be a worst case scenario,
> so I expect it to show the most improvement. For ordinary block
> allocations, I don't expect that big of an improvement.
>
> Regards,
>
> Bob Peterson
> Red Hat File Systems

That looks very encouraging I think, definitely a good step forward.
Acked-by: Steven Whitehouse <swhiteho@redhat.com>

Steve.