From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stefano Brivio <sbrivio@redhat.com>
To: passt-dev@passt.top
Subject: Re: Weird timeout issue with passt
Date: Thu, 23 Jun 2022 11:32:12 +0200
Message-ID: <20220623113212.727162c6@elisabeth>
In-Reply-To: <YrQBOFWthrYYC31a@yekko>
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On Thu, 23 Jun 2022 15:59:20 +1000
David Gibson <david(a)gibson.dropbear.id.au> wrote:

> I alluded to this in my last patchset, but here's the information I've
> gathered on the current problem I'm hitting running the passt distro
> tests.  It's pretty weird.
> 
> On at least two occasions the tests have stalled during the Fedora 30,
> aarch64 test, with the guest getting a timeout downloading the package
> lists before installing new packages.  For me this is selecting the
> mirror mirror.2degrees.nz.  I'm not sure which factors are are
> relevant to reproducing the problem though.
> 
> * The problem seems to me that the download suddenly stops progressing
> * partway through, causing dnf to eventually time out
> 
> * If I manually try a "dnf clean all && dnf makecache -v" using the
>   same guest image, it  doesn't fail every time, but it fails
>   significantly more often than not
> 
> * It doesn't fail on the same file every time
> 
> * I haven't been able to reproduce manually downloading the failing
>   file with curl (tried repeatedly)
> 
> * If I restrict dnf to a single repository rather than the whole set,
>   I haven't managed to reproduce the problem

If I remember correctly, dnf downloads from multiple repositories at
the same time, which might explain these two points.

> 
> * If I use qemu's -net user slirp instead of passt with the same disk
>   image , I haven't been able to reproduce the problem (tried a bunch
>   of times)
> 
> * I've reproduced with the guest using both IPv4 and IPv6
> 
> * I have reproduced what looks like the same problem with an x86 guest
>   image under KVM (also Fedora 30), but it seems to happen much less
>   often (seen once in 10 or more attempts)
> 
> * Seems to reproduce fairly readily with an x86 guest under TCG
>   though, so I'm guessing the difference is timing related.

...hmm, I never hit this, and I guess our versions of qemu eventually
crossed at some point -- I'm using 7.0.50 (v7.0.0-937-gd6900f445e)
right now.

Passing a capture file via --pcap for that instance of passt (started
at the beginning of fedora/tests) might help shine some light on this.
You could also add run ./test with PCAP=1, but that would capture
everything, which will take a ton of space.

-- 
Stefano


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