[Cluster-devel] [PATCH 0/2] GFS2: inplace_reserve performance improvements

[Bob Peterson <rpeterso@redhat.com>]

----- Original Message -----
> Thanks for that Bob, we've been watching with interest the changes going in
> upstream but at the moment we're not really in a position to take advantage
> of them.
> 
> Due to hardware vendor support certification requirements XenServer can only
> very occasionally make big kernel bumps that would affect the ABI that the
> driver would see as that would require our hardware partners to recertify.
> So, we're currently on a 4.4.52 base but the gfs2 driver is somewhat newer
> as it is essentially self-contained and therefore we can backport change
> more easily. We currently have most of the GFS2 and DLM changes that are in
> 4.15 backported into the XenServer 7.6 kernel, but we can't take the ones
> related to iomap as they are more invasive and it looks like a number of the
> more recent performance targeting changes are also predicated on the iomap
> framework.
> 
> As I mentioned in the covering letter, the intra host problem would largely
> be a non-issue if EX glocks were actually a host wide thing with local
> mutexes used to share them within the host. I don't know if this is what
> your patch set is trying to achieve or not. It's not so much that that
> selection of resource group is "random", just that there is a random chance
> that we won't select the first RG that we test, it probably does work out
> much the same though.
> 
> The inter host problem addressed by the second patch seems to be less
> amenable to avoidance as the hosts don't seem to have a synchronous view of
> the state of the resource group locks (for understandable reasons as I'd
> expect thisto be very expensive to keep sync'd). So it seemed reasonable to
> try to make it "expensive" to request a resource that someone else is using
> and also to avoid immediately grabbing it back if we've been asked to
> relinquish it. It does seem to give a fairer balance to the usage without
> being massively invasive.
> 
> We thought we should share these with the community anyway even if they only
> serve as inspiration for more detailed changes and also to describe the
> scenarios where we're seeing issues now that we have completed implementing
> the XenServer support for GFS2 that we discussed back in Nuremburg last
> year. In our testing they certainly make things better. They probably aren?t
> fully optimal as we can't maintain 10g wire speed consistently across the
> full LUN but we're getting about 75% which is certainly better than we were
> seeing before we started looking at this.
> 
> Thanks,
> 
> 	Mark.

Hi Mark,

I'm really curious if you guys tried the two patches I posted here from
17 January 2018 in place of the two patches you posted. We see much better
throughput with those over stock.

I know Steve wants a different solution, and in the long run it will be a
better one, but I've been trying to convince him we should use them as a
stop-gap measure to mitigate this problem until we get a more proper solution
in place (which is obviously taking some time, due to unforeseen circumstances).

Regards,

Bob Peterson