[Gluster-devel] performance issues Manoj found in EC testing

[Manoj Pillai]

----- Original Message -----
> From: "Raghavendra Gowdappa" <rgowdapp at redhat.com>
> To: "Pranith Kumar Karampuri" <pkarampu at redhat.com>
> Cc: "Gluster Devel" <gluster-devel at gluster.org>
> Sent: Monday, June 27, 2016 12:48:49 PM
> Subject: Re: [Gluster-devel] performance issues Manoj found in EC testing
> 
> 
> 
> ----- Original Message -----
> > From: "Pranith Kumar Karampuri" <pkarampu at redhat.com>
> > To: "Xavier Hernandez" <xhernandez at datalab.es>
> > Cc: "Gluster Devel" <gluster-devel at gluster.org>
> > Sent: Monday, June 27, 2016 12:42:35 PM
> > Subject: Re: [Gluster-devel] performance issues Manoj found in EC testing
> > 
> > 
> > 
> > On Mon, Jun 27, 2016 at 11:52 AM, Xavier Hernandez < xhernandez at datalab.es
> > >
> > wrote:
> > 
> > 
> > Hi Manoj,
> > 
> > I always enable client-io-threads option for disperse volumes. It improves
> > performance sensibly, most probably because of the problem you have
> > detected.
> > 
> > I don't see any other way to solve that problem.
> > 
> > I agree. Updated the bug with same info.
> > 
> > 
> > 
> > I think it would be a lot better to have a true thread pool (and maybe an
> > I/O
> > thread pool shared by fuse, client and server xlators) in libglusterfs
> > instead of the io-threads xlator. This would allow each xlator to decide
> > when and what should be parallelized in a more intelligent way, since
> > basing
> > the decision solely on the fop type seems too simplistic to me.
> > 
> > In the specific case of EC, there are a lot of operations to perform for a
> > single high level fop, and not all of them require the same priority. Also
> > some of them could be executed in parallel instead of sequentially.
> > 
> > I think it is high time we actually schedule(for which release) to get this
> > in gluster. May be you should send out a doc where we can work out details?
> > I will be happy to explore options to integrate io-threads, syncop/barrier
> > with this infra based on the design may be.
> 
> +1. I can volunteer too.

Thanks, folks! As a quick update, throughput on a single client test jumped 
from ~180 MB/s to 700+MB/s after enabling client-io-threads. Throughput is 
now more in line with what is expected for this workload based on 
back-of-the-envelope calculations.

Are there any reservations about recommending client-io-threads=on as 
"default" tuning, until the enhancement discussed above becomes reality? 

-- Manoj

> 
> > 
> > 
> > 
> > Xavi
> > 
> > 
> > On 25/06/16 19:42, Manoj Pillai wrote:
> > 
> > 
> > 
> > ----- Original Message -----
> > 
> > 
> > From: "Pranith Kumar Karampuri" < pkarampu at redhat.com >
> > To: "Xavier Hernandez" < xhernandez at datalab.es >
> > Cc: "Manoj Pillai" < mpillai at redhat.com >, "Gluster Devel" <
> > gluster-devel at gluster.org >
> > Sent: Thursday, June 23, 2016 8:50:44 PM
> > Subject: performance issues Manoj found in EC testing
> > 
> > hi Xavi,
> > Meet Manoj from performance team Redhat. He has been testing EC
> > performance in his stretch clusters. He found some interesting things we
> > would like to share with you.
> > 
> > 1) When we perform multiple streams of big file writes(12 parallel dds I
> > think) he found one thread to be always hot (99%CPU always). He was asking
> > me if fuse_reader thread does any extra processing in EC compared to
> > replicate. Initially I thought it would just lock and epoll threads will
> > perform the encoding but later realized that once we have the lock and
> > version details, next writes on the file would be encoded in the same
> > thread that comes to EC. write-behind could play a role and make the writes
> > come to EC in an epoll thread but we saw consistently there was just one
> > thread that is hot. Not multiple threads. We will be able to confirm this
> > in tomorrow's testing.
> > 
> > 2) This is one more thing Raghavendra G found, that our current
> > implementation of epoll doesn't let other epoll threads pick messages from
> > a socket while one thread is processing one message from that socket. In
> > EC's case that can be encoding of the write/decoding read. This will not
> > let replies of operations on different files to be processed in parallel.
> > He thinks this can be fixed for 3.9.
> > 
> > Manoj will be raising a bug to gather all his findings. I just wanted to
> > introduce him and let you know the interesting things he is finding before
> > you see the bug :-).
> > --
> > Pranith
> > 
> > Thanks, Pranith :).
> > 
> > Here's the bug: https://bugzilla.redhat.com/show_bug.cgi?id=1349953
> > 
> > Comparing EC and replica-2 runs, the hot thread is seen in both cases, so
> > I have not opened this as an EC bug. But initial impression is that
> > performance impact for EC is particularly bad (details in the bug).
> > 
> > -- Manoj
> > 
> > 
> > 
> > 
> > --
> > Pranith
> > 
> > _______________________________________________
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