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

[Raghavendra Gowdappa]

----- 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.

> 
> 
> 
> 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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