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On Tue, Jun 30, 2020, at 1:20 AM, Fabian Groffen wrote: |
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> Hi, |
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> |
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> On 29-06-2020 21:13:43 -0500, Sid Spry wrote: |
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> > Hello, |
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> > |
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> > I have some runnable pseudocode outlining a faster tree verification algorithm. |
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> > Before I create patches I'd like to see if there is any guidance on making the |
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> > changes as unobtrusive as possible. If the radical change in algorithm is |
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> > acceptable I can work on adding the changes. |
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> > |
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> > Instead of composing any kind of structured data out of the portage tree my |
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> > algorithm just lists all files and then optionally batches them out to threads. |
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> > There is a noticeable speedup by eliding the tree traversal operations which |
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> > can be seen when running the algorithm with a single thread and comparing it to |
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> > the current algorithm in gemato (which should still be discussed here?). |
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> |
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> I remember something that gemato used to use multiple threads, but |
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> because it totally saturated disk-IO, it was brought back to a single |
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> thread. People were complaining about unusable systems. |
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> |
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I think this is an argument for cgroups limits support on the portage process or |
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account as opposed to an argument against picking a better algorithm. That is |
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something I have been working towards, but I am only one man. |
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> In any case, can you share your performance results? What speedup did |
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> you see, on warm and hot FS caches? Which type of disk do you use? |
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> |
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I ran all tests multiple times to make them warm off of a Samsung SSD, but |
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nothing very precise yet. |
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% gemato verify --openpgp-key signkey.asc /var/db/repos/gentoo |
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[...] |
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INFO:root:Verifying /var/db/repos/gentoo... |
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INFO:root:/var/db/repos/gentoo verified in 16.45 seconds |
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sometimes going higher, closer to 18s, vs. |
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% ./veriftree.py |
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4.763171965983929 |
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So roughly an order of magnitude speedup without batching to threads. |
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> You could compare against qmanifest, which uses OpenMP-based |
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> paralllelism while verifying the tree. On SSDs this does help. |
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> |
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I lost my notes -- how do I specify to either gemato or qmanifest the GnuPG |
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directory? My code is partially structured as it is because I had problems doing |
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this. I rediscovered -K/--openpgp-key in gemato but am unsure for qmanifest. |
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