linux-kernel - Re: [PATCH] NFSv4: Use exponential backoff delay for NFS4

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Message-ID: <20130425134918.GC31851@fieldses.org>
Date:	Thu, 25 Apr 2013 09:49:18 -0400
From:	"bfields@...ldses.org" <bfields@...ldses.org>
To:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
Cc:	David Wysochanski <dwysocha@...hat.com>,
	Dave Chiluk <chiluk@...onical.com>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] NFSv4: Use exponential backoff delay for NFS4_ERRDELAY

On Thu, Apr 25, 2013 at 01:30:58PM +0000, Myklebust, Trond wrote:
> On Thu, 2013-04-25 at 09:29 -0400, bfields@...ldses.org wrote:
> 
> > My position is that we simply have no idea what order of magnitude even
> > delay should be.  And that in such a situation exponential backoff such
> > as implemented in the synchronous case seems the reasonable default as
> > it guarantees at worst doubling the delay while still bounding the
> > long-term average frequency of retries.
> 
> So we start with a 15 second delay, and then go to 60 seconds?

I agree that a server should normally be doing the wait on its own if
the wait would be on the order of an rpc round trip.

So I'd be inclined to start with a delay that was an order of magnitude
or two more than a round trip.

And I'd expect NFS isn't common on networks with 1-second latencies.

So the 1/10 second we're using in the synchronous case sounds closer to
the right ballpark to me.

--b.
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