From: Will Springer <skirmisher@protonmail•com>
To: linuxppc-dev@lists•ozlabs.org
Cc: daniel@octaforge•org
Subject: CONFIG_PPC_VAS depends on 64k pages...?
Date: Thu, 19 Nov 2020 10:58:39 +0000 [thread overview]
Message-ID: <7171078.EvYhyI6sBW@sheen> (raw)
I learned about the POWER9 gzip accelerator a few months ago when the
support hit upstream Linux 5.8. However, for some reason the Kconfig
dictates that VAS depends on a 64k page size, which is problematic as I
run Void Linux, which uses a 4k-page kernel.
Some early poking by others indicated there wasn't an obvious page size
dependency in the code, and suggested I try modifying the config to switch
it on. I did so, but was stopped by a minor complaint of an "unexpected DT
configuration" by the VAS code. I wasn't equipped to figure out exactly what
this meant, even after finding the offending condition, so after writing a
very drawn-out forum post asking for help, I dropped the subject.
Fast forward to today, when I was reminded of the whole thing again, and
decided to debug a bit further. Apparently the VAS platform device
(derived from the DT node) has 5 resources on my 4k kernel, instead of 4
(which evidently works for others who have had success on 64k kernels). I
have no idea what this means in practice (I don't know how to introspect
it), but after making a tiny patch[1], everything came up smoothly and I
was doing blazing-fast gzip (de)compression in no time.
Everything seems to work fine on 4k pages. So, what's up? Are there
pitfalls lurking around that I've yet to stumble over? More reasonably,
I'm curious as to why the feature supposedly depends on 64k pages, or if
there's anything else I should be concerned about.
I do have to say I'm quite satisfied with the results of the NX
accelerator, though. Being able to shuffle data to a RaptorCS box over gigE
and get compressed data back faster than most software gzip could ever
hope to achieve is no small feat, let alone the instantaneous results locally.
:)
Cheers,
Will Springer [she/her]
[1]: https://github.com/Skirmisher/void-packages/blob/vas-4k-pages/srcpkgs/linux5.9/patches/ppc-vas-on-4k.patch
next reply other threads:[~2020-11-19 11:09 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-19 10:58 Will Springer [this message]
2020-11-19 14:43 ` CONFIG_PPC_VAS depends on 64k pages...? Christophe Leroy
2020-12-01 5:52 ` Sukadev Bhattiprolu
2020-12-01 13:16 ` Bulent Abali
2020-12-02 7:17 ` Will Springer
2021-01-15 13:54 ` Carlos Eduardo de Paula
2020-12-01 21:05 ` Carlos Eduardo de Paula
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