Date:   Tue, 28 Sep 2021 19:18:31 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc:     Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH 0/3] get_abi: improve message output and fix a regression

On Tue, Sep 28, 2021 at 02:27:39PM +0200, Mauro Carvalho Chehab wrote:
> Em Tue, 28 Sep 2021 13:04:22 +0200
> Greg Kroah-Hartman <gregkh@...uxfoundation.org> escreveu:
> 
> > On Tue, Sep 28, 2021 at 12:14:01PM +0200, Mauro Carvalho Chehab wrote:
> > > Hi Greg,
> > > 
> > > As promised on
> > > 
> > > 	https://lore.kernel.org/lkml/20210928120304.62319fba@coco.lan/T/#u
> > > 
> > > I'm adding progress info when  get_abi.pl is checking for undefined ABI symbols
> > > on patches 1 and 2.
> > > 
> > > That will help not only to identify what is causing delays on the script, but also
> > > to notify the user that processing it could take some time on some systems.
> > > 
> > > If you run it on your big server with:
> > > 
> > >   scripts/get_abi.pl undefined 2>logs
> > > 
> > > The "logs" file will contain timestamps relative to the time the script started to
> > > do the regex matches for sysfs files. It should be printing one line every
> > > time the progress completes 1% or one second after the last progress output.  
> > 
> > Adding more debugging and tweaking the script a bit to show the file it
> > is about to check, not the one it finished checking,
> 
> Feel free to modify the script and add such debug/tweaks if you find
> it useful. 
> 
> > I got the following
> > debug output that seems to pinpoint the problem file.
> > 
> > The sysfs file that is causing problems is:
> > 	/sys/devices/pci0000:40/0000:40:00.2/iommu/ivhd1/amd-iommu/cap
> > 
> > and here's some debugging output for the regex it needs to search for
> > this:
> > 
> > /sys/devices/pci0000:40/0000:40:00.2/iommu/ivhd1/amd-iommu/cap =~ /^(?^:^/sys/class/iommu/.*/amd\-iommu/cap$)$/
> > /sys/devices/pci0000:40/0000:40:00.2/iommu/ivhd1/amd-iommu/cap =~ /^(?^:^/sys/class/iommu/.*/intel\-iommu/cap$)$/
> > /sys/devices/pci0000:40/0000:40:00.2/iommu/ivhd1/amd-iommu/cap =~ /^(?^:^/sys/devices/pci.*.*.*.*\:.*.*/0000\:.*.*\:.*.*..*/dma/dma.*chan.*/quickdata/cap$)$/
> > /sys/devices/pci0000:40/0000:40:07.0/iommu/amd-iommu/cap =~ /^(?^:^/sys/class/iommu/.*/amd\-iommu/cap$)$/
> > /sys/devices/pci0000:40/0000:40:07.0/iommu/amd-iommu/cap =~ /^(?^:^/sys/class/iommu/.*/intel\-iommu/cap$)$/
> > /sys/devices/pci0000:40/0000:40:07.0/iommu/amd-iommu/cap =~ /^(?^:^/sys/devices/pci.*.*.*.*\:.*.*/0000\:.*.*\:.*.*..*/dma/dma.*chan.*/quickdata/cap$)$/
> > /sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:02/device:7a/physical_node/iommu/ivhd1/amd-iommu/cap =~ /^(?^:^/sys/class/iommu/.*/amd\-iommu/cap$)$/
> > /sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:02/device:7a/physical_node/iommu/ivhd1/amd-iommu/cap =~ /^(?^:^/sys/class/iommu/.*/intel\-iommu/cap$)$/
> > /sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:02/device:7a/physical_node/iommu/ivhd1/amd-iommu/cap =~ /^(?^:^/sys/devices/pci.*.*.*.*\:.*.*/0000\:.*.*\:.*.*..*/dma/dma.*chan.*/quickdata/cap$)$/
> > /sys/devices/pci0000:40/0000:40:01.3/0000:4a:00.0/0000:4b:0a.0/0000:50:00.0/iommu/amd-iommu/cap =~ /^(?^:^/sys/class/iommu/.*/amd\-iommu/cap$)$/
> > /sys/devices/pci0000:40/0000:40:01.3/0000:4a:00.0/0000:4b:0a.0/0000:50:00.0/iommu/amd-iommu/cap =~ /^(?^:^/sys/class/iommu/.*/intel\-iommu/cap$)$/
> > /sys/devices/pci0000:40/0000:40:01.3/0000:4a:00.0/0000:4b:0a.0/0000:50:00.0/iommu/amd-iommu/cap =~ /^(?^:^/sys/devices/pci.*.*.*.*\:.*.*/0000\:.*.*\:.*.*..*/dma/dma.*chan.*/quickdata/cap$)$/
> 
> Hmm... interesting. Perhaps the problem is on regexes like this:
> 
> 	/^(?^:^/sys/devices/pci.*.*.*.*\:.*.*/0000\:.*.*\:.*.*..*/dma/dma.*chan.*/quickdata/cap$)$/
> 
> Which actually represents this What:
> 	/sys/devices/pciXXXX:XX/0000:XX:XX.X/dma/dma<n>chan<n>/quickdata/cap
> 
> The script could have done a better job escaping "." character on
> it (but that is not too trivial) and grouping altogether ".*" 
> repetitions, although, in this specific case, probably the best
> regex would be, instead:
> 
> 	/sys/devices/pci[\da-f:\.]+/dma/dma\d+chan\d+/quickdata/cap
> 
> One possible long-term solution would be to directly use regexes 
> directly on "What" fields inside Documentation/ABI, but on some parts
> this would require some changes, like, for instance:
> 
> 	/sys/bus/usb/devices/<busnum>-<devnum>:<config num>.<interface num>/<hid-bus>:<vendor-id>:<product-id>.<num>/kone/roccatkone<minor>/weight
> 
> Ok, we could likely use capture groups like:
> 
> 	(?<NAME>pattern)
> 
> but IMO that would make it a lot harder to be understood by humans.
> 
> 
> > And sometimes this thing finishes in 20 seconds, and others, many many
> > minutes.  It's not deterministic at all, which is odd.  Is the sysfs
> > tree being sorted so that this should always have the same search order?
> 
> No, because it uses a lot of hashes in order to speed it up. Yet,
> it shouldn't be hard - nor it would significantly affect the processing
> time - to make it more deterministic. See the enclosed path.

That patch solved everything.

It now only takes 10 seconds.  Every time.  Without the patch, it feels
hung for some reason.

Care to turn that into a patch that I can take?

> > Anyway, I've applied this series as well, this helps in finding the
> > problems :)
> 
> Thanks!
> 
> > Note, I can provide an off-list tarball of /sys/ if that would help in
> > debugging anything on your end.
> 
> Yeah, that can help. Feel free to send it to me.
> 
> Btw, I just got an arm64 server with 128 CPUs for testing. I'm trying
> to allocate also a big x86 server here, but I'm not sure if it is AMD or
> Intel.

This is on perl 5.34 here.

thanks,

greg k-h

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