Date: Sat, 4 Feb 2012 15:43:19 -0800 From: John-Mark Gurney <jmg@funkthat.com> To: Ian Lepore <freebsd@damnhippie.dyndns.org> Cc: freebsd-arm@freebsd.org Subject: Re: Performance of SheevaPlug on 8-stable Message-ID: <20120204234319.GR52468@funkthat.com> In-Reply-To: <1328030999.1662.324.camel@revolution.hippie.lan> References: <1327980703.1662.240.camel@revolution.hippie.lan> <F48E21E0-129A-418A-B147-7D5FB01160A8@bsdimp.com> <1328025245.1662.289.camel@revolution.hippie.lan> <5FB4965A-66C9-4C99-8B61-5AC605F9ECC5@bsdimp.com> <1328030999.1662.324.camel@revolution.hippie.lan>
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Ian Lepore wrote this message on Tue, Jan 31, 2012 at 10:29 -0700:
> On Tue, 2012-01-31 at 09:37 -0700, Warner Losh wrote:
> > On Jan 31, 2012, at 8:54 AM, Ian Lepore wrote:
> >
> > > On Mon, 2012-01-30 at 22:39 -0700, Warner Losh wrote:
> > >> Hi Ian,
> > >>
> > >> Do you have any data on what 9.0 does?
> > >>
> > >> Warner
> > >
> > > No. Do you have reason to believe it will be different than 8.x?
> > >
> > > It would be a major effort right now to get anything later than 8.2
> > > built and running on one of our arm platforms. Maybe not as hard as the
> > > 6.2 -> 8.2 conversion was, but we're still carrying a lot of diffs from
> > > stock FreeBSD that have to be analyzed and merged by hand. Actually
> > > before that can even happen I'd have to grab a snapshot of 9.0 and do an
> > > svn->Hg conversion to even be able to start merging the diffs (and I'm
> > > hardly an Hg expert, but those in the company who are let me know last
> > > week that they're just as busy as me, and I'm on my own for this kind of
> > > work). It's work I want to do, but I suspect it's going to happen later
> > > rather than sooner because product deadlines are beginning to loom and
> > > my ability to spend most of my time working on the OS side of things is
> > > waning.
> > >
> > > If there are some specific changes you've got in mind that affect this
> > > problem I might be able to backport and test them faster than I could
> > > get a full 9.0 or -current build environment working, just point me at
> > > them.
> >
> > I thought that we'd done a root cause of this and had put a fix into the vm system. Lemme look...
> >
> > ------------------------------------------------------------------------
> > r224049 | marcel | 2011-07-14 20:11:26 -0600 (Thu, 14 Jul 2011) | 2 lines
> >
> > In pmap_protect(), don't call vm_page_dirty() if the page is unmanaged.
> >
> >
> > ------------------------------------------------------------------------
> > r221844 | cognet | 2011-05-13 09:54:12 -0600 (Fri, 13 May 2011) | 4 lines
> >
> > In pmap_change_wiring(), use the right argument for pmap_modify_pv().
> > It only worked because the only consumer calls pmap_change_wiring() to remove
> > the wiring.
> >
> > ------------------------------------------------------------------------
> > r212507 | cognet | 2010-09-12 14:46:32 -0600 (Sun, 12 Sep 2010) | 5 lines
> >
> > In pmap_remove_all(), do not decrease pm_stats.wired_count if the mapping was
> > wired, as it's been done later in pmap_nuke_pv().
> >
> > Submitted by: Mark Tinguely
> >
> >
> > ------------------------------------------------------------------------
> > r209223 | cognet | 2010-06-15 16:16:02 -0600 (Tue, 15 Jun 2010) | 4 lines
> >
> > Turn off cache if there's more than one kernel mapping, and one is writable.
> >
> > Submitted by: Mark Tinguely
> >
> > ------------------------------------------------------------------------
> > r205028 | raj | 2010-03-11 14:16:54 -0700 (Thu, 11 Mar 2010) | 12 lines
> >
> > Fix ARM cache handling yet more.
> >
> > 1) vm_machdep.c: remove the dangling allocations so they do not
> > un-necessarily turn off the cache upon consecutive access.
> >
> > 2) busdma_machdep.c: remove the same amount than shadow mapped.
> >
> > Reported by: Maks Verver
> > Submitted by: Mark Tinguely
> > Reviewed by: Grzegorz Bernacki
> > MFC after: 3 days
> >
> > ------------------------------------------------------------------------
> > r203637 | raj | 2010-02-07 13:48:57 -0700 (Sun, 07 Feb 2010) | 19 lines
> >
> > Improve checking whether an ARM VA has a valid mapping before performing cache
> > sync.
> >
> > VIPT/PIPT caches need valid VA-PA mapping in PTE for a cache operation to
> > succeed (unlike VIVT). Prior to this fix pmap was using l2pte_valid() for that
> > check, but this is not sufficient as the function merely checks if a PTE
> > exists (there can be existing but _invalid_ entries in the table).
> >
> > A new pmap_has_valid_mapping() routine is introduced to do this job right by
> > checking proper PTE flags.
> >
> > Among other potential problems this cures coherency issues with L2 caches on
> > MV-78100.
> >
> > Submitted by: Grzegorz Bernacki, Piotr Ziecik
> > Reviewed, tested by: marcel
> > Obtained from: Semihalf
> > MFC after: 1 week
> >
> >
> > Only the last two have MFC, so you can start there and see which of these changes are in...
> >
> > Just thought you might have a reference board that would be easy to test...
> >
> > Warner
>
> I think we may have all those changes incorporated except perhaps
> r224049; I'll make sure of that.
>
> r209223 is the change that exposed this situation.
>
> I'm skeptical that any of the changes you cite (or any change at all in
> the pmap layer) will fix the problem, because the problem seems to be
> rooted in the fact that the vfs buffer cache establishes a kva mapping
> of the buffer pages with the protections set to READ|WRITE|EXEC and
> leaves that mapping in place as long as the buffer is in the cache, and
> r209223 says that as long as there are multiple mappings of a page with
> at least one writable, that page's i-cache and d-cache bits stay off.
> (The multiple mappings being the one for the buffer cache that includes
> write access and one or more READ|EXEC mappings made by pmap() when the
> executable or library is loaded/relocated.)
>
> If my analysis is correct (and I'm fairly sure, if not 100% positive,
> that it is), then it seems to me that the only fix available is going to
> be at the vfs layer, and it's going to involve dropping the write access
> to the pages in the buffer cache once any physical IO and/or uio
> operations needing write access are completed.
>
> Even if I could figure out a patchset to fix the problem, it's going to
> need a lot of input from the vm gurus to answer questions such as what
> the performance impact will be to non-VIVT platforms that don't need
> this extra work done. If the extra work is expensive enough (and I'm
> not sure I could evaluate that properly) it may need to be conditional
> on whether the platform needs it. I'm also vaguely uneasy with all this
> on a purely philosphical level, since this could end up basically
> infecting MI code with a platform-specific concept.
What is an easy to figure out if a system we have is effected by this
issue? I have a GW2348-4 board running FreeBSD 9.0-RC1 w/ some minor
modifications to get pf to work...
I think the system is effected by this since userland seems really slow..
Thanks.
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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