"Will Deacon" <will.deacon(a)arm.com> wrote on 02/16/2011 01:07:09 PM:
> > I've now built a kernel with CONFIG_ARM_ERRATA_720789 enabled, and the
> > symptoms indeed seem to have disappeared completely ...
>
> Yup - that's because without it, invalidating a TLB entry for a
particular
> process isn't broadcast correctly, so you can end up using the old
(pre-COW)
> mappings if you're running on a different core.
OK. So I guess the only remaining questions is: if this hardware needs the
errata fix to work properly, shouldn't it be automatically selected by the
kernel configure logic? Note that this appears to happen for certain OMAP
boards, see arch/arm/mach-omap2/Kconfig:
config ARCH_OMAP4
bool "TI OMAP4"
default y
depends on ARCH_OMAP2PLUS
select CPU_V7
select ARM_GIC
select PL310_ERRATA_588369
select ARM_ERRATA_720789 <<=====
select USB_ARCH_HAS_EHCI
But this does not happen for the vexpress; arch/arm/mach-vexpress/Kconfig
has only:
config ARCH_VEXPRESS_CA9X4
bool "Versatile Express Cortex-A9x4 tile"
select CPU_V7
select ARM_GIC
Mit freundlichen Gruessen / Best Regards
Ulrich Weigand
--
Dr. Ulrich Weigand | Phone: +49-7031/16-3727
STSM, GNU compiler and toolchain for Linux on System z and Cell/B.E.
IBM Deutschland Research & Development GmbH
Vorsitzender des Aufsichtsrats: Martin Jetter | Geschäftsführung: Dirk
Wittkopp
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Stuttgart, HRB 243294
Hello,
* Continue looking into DENbench benchmarks.
* While testing SMS I realized that my current implementation of doloop
pattern for ARM does not follow SMS's requirement to have the doloop
instructions be decoupled from the other loop's instructions. This happens
because doloop uses CC register which might be used elsewhere in the loop.
I am looking into a solution for that.
Thanks,
Revital
Hi,
This week I looked into DENBench:
* sad8_c (hot function from mp4encode) needs SLP reduction, but it
also contains cond_expr which cannot be vectorized as reduction, so I
don't think there is anything I can do here
* fdct_int32 (another hot function from mp4encode) now gets vectorized
with vzip/vuzp patch, but the vectorization causes performance
degradation here because of multiple register spills. I also noticed
that vectorizer costs are not set for NEON, i.e., it uses default
costs. So, I am now working on costs for NEON and adding registers
consideration into vectorizer's cost model.
I also did some general vectorization research, checking opportunities
of collaboration with GRAPHITE pass and auto-parallelization.
Ira
I mentioned in the toolchain standup call that I'd done a quick
estimate of the work required to support vexpress, so I thought I
might as well clean it up a little and post it.
This is a quick summary and time estimate for adding Versatile
Express support to qemu. The general idea is that most of the
components on this board already have QEMU implementations
(since they're standard ARM primecells used in versatile/realview),
and we can live without the few major components that aren't
implemented (maybe we'd need dummy implementations if the
kernel prods them on startup.)
Components already supported by QEMU:
-------------------------------------
A9MPx4
PL050 keyboard, mouse
SMCS LAN9118 ethernet
PL011 UARTs
SP804 timers
Components with a near match in QEMU:
-------------------------------------
PL111 CLCD -- qemu has a PL110
PL180 MMC card -- qemu has a PL181
-- both cases should either just work or be fairly trivial tweaks
Components not supported by QEMU:
---------------------------------
PL041 audio
compact flash
two-wire serial bus (for PCI-express switch config and DVI-I displays)
ISP1761 Philips USB controller
User switches and LEDs -- vexpress specific, but trivial to do
Components where a dummy implementation should be sufficient:
-------------------------------------------------------------
PL310 L2 cache controller
PL341 dynamic memory controller
PL354 static memory bus controller
trustzone controllers
Other required work:
--------------------
The usual knitting for interrupts, clocks, reset etc etc.
Summary
-------
Assuming we're happy not to worry about support for
audio, USB, two-wire serial bus or compact flash, this
is about two weeks work to put together, test and get
a more-or-less upstreamable patchset from. This would
produce a platform hopefully at least as usable as
versatile, but with an A9 and 1GB RAM.
-- PMM
"Will Deacon" <will.deacon(a)arm.com> wrote on 02/14/2011 11:30:45 AM:
> > - In testing on Versatile Express, I noticed what appears to be SMP
> > related bugs in handling regular software breakpoints: occasionally,
> > software breakpoints simply are not hit and execution continues as if
> > the underlying code had not been changed at all. This symptom
> > completely goes away if GDB and the debugged process are forced to
> > the same CPU using the affinity feature (e.g. with schedtool).
>
> I've seen this issue in the past but I thought I'd fixed it. What kernel
are
> you using and do you have CONFIG_ARM_ERRATA_720789 enabled?
I'm using the 2.6.37-1002-linaro-vexpress kernel from the Linaro package
of the same name. This does *not* have CONFIG_ARM_ERRATA_720789 enabled
(presumably because the mach-vexpress/Kconfig file does not add it?) ...
> > My guess, just from seeing those symptoms, would be that when
inserting
> > a software breakpoint via ptrace, not all i-caches on all CPUs are
> > reliably flushed ... Any thoughts on this?
>
> There was an I-cache aliasing problem in the kernel coupled with a TLB
> invalidation hardware bug on the versatile express. I fixed these though
> and haven't seen any problems since.
Hmm, a TLB flush problem could also explain the symptom (because the write
of the breakpoint to the text section causes a copy-on-write operation
which
installs a new page ...)
I'll try rebuilding the kernel with the above config option enabled.
> Hmmm, I'll need to have a think about this. What does GDB do if it
receives
> a SIGTRAP with si_addr set to (potentially) complete nonsense? As an
aside,
> Cortex-A15 reports the faulting address for a watchpoint correctly, so we
> will be able to use multiple watchpoints there.
The GDB common core can handle either of the following two indications:
A) The (read/write/access) watchpoint at address XXX triggered.
B) A write watchpoint may have triggered at some address.
In the case of B, GDB will scan all the write breakpoints it is currently
tracking and compare the current value at that address with the last value
it remembers being present there. Any changes GDB sees will cause it to
report the corresponding watchpoint as triggered.
As far as the kernel interface is concerned, the important issue that the
ARM native target in GDB is able to understand what the kernel reports, so
it can in turn report either case A or B to the common core.
This means as long as there is some way for GDB to understand the kernel
is reporting a write watchpoint hit at an unknown address, everything is
fine. This could be done e.g. be reporting a "slot" zero in si_errno to
indicate the slot (and then also the address) triggering the watchpoint
is unknown ...
> > - Finally, I noticed when reading kernel code that under some
> > circumstances, the kernel will automatically do a single step to
> > get off a watchpoint that was just hit. However, this does not
> > happen for user-space watchpoints installed via ptrace, right?
> > (Just wanting to confirm; since GDB currently does that single
> > step itself -- we don't want *both* kernel and GDB to issue a
> > single step each ...)
>
> If the {break,watch}point has been inserted via ptrace, the kernel will
> send a SIGTRAP instead of stepping the instruction.
OK, thanks for the confirmation!
> > I haven't gotten to looking further into other hardware (IGEP,
> > Panda) -- that's next on the list.
>
> Good stuff, keep me posted if you see any further problems!
Sure, will do!
Mit freundlichen Gruessen / Best Regards
Ulrich Weigand
--
Dr. Ulrich Weigand | Phone: +49-7031/16-3727
STSM, GNU compiler and toolchain for Linux on System z and Cell/B.E.
IBM Deutschland Research & Development GmbH
Vorsitzender des Aufsichtsrats: Martin Jetter | Geschäftsführung: Dirk
Wittkopp
Sitz der Gesellschaft: Böblingen | Registergericht: Amtsgericht
Stuttgart, HRB 243294
Hello, my fellow ARM aficionados!
The Linaro Developer Platform Team is pleased to announce a new initiative
to help improve the state of software on ARM: the ARM porting jam. Starting
today, February 16th, we will be running a weekly IRC jam on Wednesdays from
1400-1800 UTC to bring developers together to work on all manner of
userspace porting bugs, with the aim of fixing portability issues and
getting the fixes delivered to our upstreams.
An initial porting queue of known issues can be found here:
https://bugs.launchpad.net/ubuntu/+bugs?field.tag=arm-porting-queue
Interested in making the software in Ubuntu run better on ARM? Stop on by
the #linaro channel on irc.linaro.org today!
--
Steve Langasek Give me a lever long enough and a Free OS
Debian Developer to set it on, and I can move the world.
Ubuntu Developer http://www.debian.org/
slangasek(a)ubuntu.com vorlon(a)debian.org
"Will Deacon" <will.deacon(a)arm.com> wrote on 02/11/2011 10:13:01 AM:
> I don't have a pandaboard, so I'd be interested to see if the code
> works there. I developed it using ARM boards, so the versatile express
> is a known good target.
I've now got it working reliably on on Versatile Express, after fixing
a couple of bugs on the GDB side (both in the HW-watchpoint patch, and
in common GDB code). The testsuite now passes with no regressions when
enabling HW watchpoints, except for two tests that require more than one
single watchpoint to be supported.
This raises another couple of issues/questions, however:
- In testing on Versatile Express, I noticed what appears to be SMP
related bugs in handling regular software breakpoints: occasionally,
software breakpoints simply are not hit and execution continues as if
the underlying code had not been changed at all. This symptom
completely goes away if GDB and the debugged process are forced to
the same CPU using the affinity feature (e.g. with schedtool).
My guess, just from seeing those symptoms, would be that when inserting
a software breakpoint via ptrace, not all i-caches on all CPUs are
reliably flushed ... Any thoughts on this?
- As mentioned above, the kernel currently only supports one single
watchpoint to be active at a time, even though hardware might support
multiple ones. The reason seems to be that when a watchpoint triggers,
the kernel cannot figure out which one it was (if there's more than one
choice).
This is a bit unfortunate, given that GDB will attempt to insert two
or more watchpoints in many interesting cases (e.g. a "watch *p"
command will insert *two* low-level watchpoints, one at the address
of p, and one at the address where p (currently) points to).
In addition, for regular (write) watchpoints, GDB does not actually
*require* the underlying hardware/kernel to specify which watchpoint
was hit; GDB is able to find out by itself by checking whether the
values at any of the currently active locations actually changed.
(For read/access type watchpoints, GDB does require that underlying
support -- but those are much more rarely used anyway.)
Do you see any chance of improving upon the current behaviour?
- Finally, I noticed when reading kernel code that under some
circumstances, the kernel will automatically do a single step to
get off a watchpoint that was just hit. However, this does not
happen for user-space watchpoints installed via ptrace, right?
(Just wanting to confirm; since GDB currently does that single
step itself -- we don't want *both* kernel and GDB to issue a
single step each ...)
I haven't gotten to looking further into other hardware (IGEP,
Panda) -- that's next on the list.
Mit freundlichen Gruessen / Best Regards
Ulrich Weigand
--
Dr. Ulrich Weigand | Phone: +49-7031/16-3727
STSM, GNU compiler and toolchain for Linux on System z and Cell/B.E.
IBM Deutschland Research & Development GmbH
Vorsitzender des Aufsichtsrats: Martin Jetter | Geschäftsführung: Dirk
Wittkopp
Sitz der Gesellschaft: Böblingen | Registergericht: Amtsgericht
Stuttgart, HRB 243294
== Linaro GCC 4.5 ==
Re merged all the patches I've had to back out of Linaro GCC due to
various test failures. I've now found all the extra fixes/patches
necessary to make them go ... I think. Tested the build and test on ARM
and x86_64.
== Linaro GCC 4.6 ==
Continued getting the 4.5 patches forward ported to 4.6. I now have
about 4 patches waiting for review upatream, or ready to be posted.
Upstream review isn't happening though. This partly due to GCC being in
stage 4, but mostly due to Richard Earshaw being on sabatical, and the
other maintainers being inactive. I can see that I'm going to have to
abandon my hopes of only merging to Linaro GCC once it's been approved
upstream, and be content with merging to Linaro once it's posted upstream.
Started another test to rebase the Linaro 4.6 branch with the latest
from upstream. Once that's done, I think I'll start merging my changes
in, and call that our baseline. (There'll still be merges from upstream,
but the history will diverge.)
----
Upstream patched requiring review:
* Thumb2 constants:
http://gcc.gnu.org/ml/gcc-patches/2010-12/msg00652.html
* Kazu's VFP testcases:
http://gcc.gnu.org/ml/gcc-patches/2011-02/msg00128.html
* Jie's thumb2 testcase fix:
http://gcc.gnu.org/ml/gcc-patches/2011-02/msg00670.html
== Week of Jan.31st--Feb.6th ==
* Vacation, Chinese New Year Holiday.
== Last week ==
* Monday (Feb.7th), last day of vacation.
* LP #711819, ICE in push_minipool_fix: this turned out to be a simple
case where a memory load alternative was not tagged with the minipool
range attributes. Patch sent upstream, awaiting approval.
* LP #709453, wrong code generated for NEON. Tracked this down and
mostly know how to fix this, but discussion with Ramana brought the
issue up that the entire idea of using NEON vmov.i32 for loading VFP
constants may not be good for A9, and unclear for A8. We probably should
just revert the patch from the Linaro tree for now.
* PR46002, IRA internal compiler error with -fira-algorithm=priority.
Been looking at this as a part of my background IRA studies. Have a
possible patch for this, plus found another assert fail ICE under ARM.
Will see if can post upstream this week.
== This week ==
* Continue to look at above unfinished issues, as well as other new ones.
== GDB ==
* Installed 2.6.37 Linaro kernel on IGEP and Versatile Express
in order to verify support for HW breakpoints/watchpoints
* Tested GDB HW watchpoints patch, fixed several bugs in the
patch and core GDB, and got it working reliably on vexpress
* Started discussion with Will Deacon (ARM) regarding possible
further enhancements to related kernel support
Mit freundlichen Gruessen / Best Regards
Ulrich Weigand
--
Dr. Ulrich Weigand | Phone: +49-7031/16-3727
STSM, GNU compiler and toolchain for Linux on System z and Cell/B.E.
IBM Deutschland Research & Development GmbH
Vorsitzender des Aufsichtsrats: Martin Jetter | Geschäftsführung: Dirk
Wittkopp
Sitz der Gesellschaft: Böblingen | Registergericht: Amtsgericht
Stuttgart, HRB 243294
