One of the vectorisation discussions from last year was about the poor
code GCC generates for vld{2,3,4}_*() and vst{2,3,4}_*(). It forces the
result of the loads onto the stack, then loads the individual pieces from
there. It does the same thing in reverse for stores.
I think there are two major problems here:
1. The result of the vld*() is a record type such as:
typedef struct int16x4x3_t
{
int16x4_t val[3];
} int16x4x3_t;
Ideally, we'd like one of these structures to be stored in a pseudo
register. However, the ARM port currently limits in-register
record types to 64 bits, so something this big is always given
BLKmode and stored on the stack.
A simple "fix" for this is to increase MAX_FIXED_MODE_SIZE.
That would do the right thing for the structures in arm_neon.h,
but wouldn't be safe in general.
2. The vld*() returns values as a single integer (such as EI mode),
while uses of the value will typically be in a vector mode such
as V4SI. CANNOT_CHANGE_MODE_CLASS doesn't allow direct
"mode-punning" between the two in VFP_REGS, so this again
forces the punning to be done on the stack.
The code in question is:
/* FPA registers can't do subreg as all values are reformatted to internal
precision. VFP registers may only be accessed in the mode they
were set. */
#define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS) \
(GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO) \
? reg_classes_intersect_p (FPA_REGS, (CLASS)) \
|| reg_classes_intersect_p (VFP_REGS, (CLASS)) \
However, the VFP restriction appears to be specific to VFPv1 --
thanks to Peter for the archaeology -- and isn't a problem for v6+.
In that case, removing this restriction is an important optimisation.
I tried the patch below on the following simple testcase:
#include "arm_neon.h"
void
foo (uint16_t *a)
{
uint16x4x3_t x, y;
x = vld3_u16 (a);
y = vld3_u16 (a + 12);
x.val[0] = vadd_u16 (x.val[0], y.val[0]);
x.val[1] = vadd_u16 (x.val[1], y.val[1]);
x.val[2] = vadd_u16 (x.val[2], y.val[2]);
vst3_u16 (a, x);
}
(not necessarily sensible!). Before the patch, -O2 produced:
sub sp, sp, #48
add r3, r0, #24
vld3.16 {d16-d18}, [r3]
vld3.16 {d20-d22}, [r0]
add r3, sp, #24
vstmia sp, {d20-d22}
vstmia r3, {d16-d18}
fldd d19, [sp, #8]
fldd d16, [sp, #0]
fldd d17, [sp, #24]
fldd d20, [sp, #32]
vadd.i16 d18, d16, d17
vadd.i16 d17, d19, d20
fldd d19, [sp, #16]
fldd d20, [sp, #40]
vadd.i16 d16, d19, d20
fstd d18, [sp, #0]
fstd d17, [sp, #8]
fstd d16, [sp, #16]
vldmia sp, {d16-d18}
vst3.16 {d16-d18}, [r0]
add sp, sp, #48
bx lr
After the patch we get:
vld3.16 {d24-d26}, [r0]
add r3, r0, #24
vld3.16 {d20-d22}, [r3]
vmov q8, q12 @ ti
vadd.i16 d17, d17, d21
vadd.i16 d16, d24, d20
vadd.i16 d18, d26, d22
vst3.16 {d16-d18}, [r0]
bx lr
The VMOV is a bit disappointing, and needs further investigation.
The first hunk fixes (2), and I think is correct. The second hunk
hacks (1), and isn't suitable in itself. I'll next try to make
arm_neon.h use built-in record types that are explicitly EImode,
which should remove the need to change MAX_FIXED_MODE_SIZE.
Richard
Index: gcc/gcc/config/arm/arm.h
===================================================================
--- gcc.orig/gcc/config/arm/arm.h
+++ gcc/gcc/config/arm/arm.h
@@ -1171,10 +1171,12 @@ enum reg_class
/* FPA registers can't do subreg as all values are reformatted to internal
precision. VFP registers may only be accessed in the mode they
were set. */
-#define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS) \
- (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO) \
- ? reg_classes_intersect_p (FPA_REGS, (CLASS)) \
- || reg_classes_intersect_p (VFP_REGS, (CLASS)) \
2+#define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS) \
+ (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO) \
+ ? (reg_classes_intersect_p (FPA_REGS, (CLASS)) \
+ || (TARGET_VFP \
+ && reg_classes_intersect_p (VFP_REGS, (CLASS)) \
+ && arm_fpu_desc->rev == 1)) \
: 0)
/* The class value for index registers, and the one for base regs. */
@@ -2458,4 +2460,6 @@ enum arm_builtins
instruction. */
#define MAX_LDM_STM_OPS 4
+#define MAX_FIXED_MODE_SIZE GET_MODE_BITSIZE (XImode)
+
#endif /* ! GCC_ARM_H */
Hi there. We've had an earthquake. Family and friends are fine but i'll be
unavailable for a few days. Services on ex.seabright.co.nz are down. I'll
cancel Wednesdays standup call.
See you soon,
-- Michael
== GDB ==
* Working with Will Deacon, identified root cause of GDB
problems running on Versatile Express in SMP mode, and
verified that Errata workaround fixes the problem
* Finished testing GDB HW watchpoints patch on vexpress,
submitted complete patch set for mainline inclusion
* Reviewed Yao's mainline patch to enable displaced
stepping in Thumb mode
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
== Last week ==
* PR46178, PR46002: both upstream issues related to the priority
coloring mode of IRA. Both patches submitted, the first already approved
and committed. Vladimir M. did mention that the priority algorithm
would be removed once his newer "cover class-less" patches goes in
during stage1. Anyways, I got more familiar with IRA during the process,
and the patches will still be applicable to 4.5/4.6.
* PR43872: incorrectly aligned VLAs under ARM. This turned out to be a
one-liner fix. Submitted upstream awaiting approval.
* Discussed on email/IRC with Revital Eres on SMS and ARM doloop pattern
issues.
* Launchpad #721021: Linaro GCC ICE under -mtune=xscale. Investigated a
bit; did not see ICE immediately, but GCC went into infinite loop (Khem
Raj, the reporter, says it runs for a while then ICEs).
* Coremark ARMv5TE vs ARMv7-A performance regression: reproduced
consistently using our own Tegra boards. Investigated and seem to have
found something, will post more detailed findings later.
== This week ==
* Coremark investigation.
* More GCC issues.
== GCC ==
Posted 2 of our 4.5 patches upstream.
My latest 4.6 build and test completed, so I've pushed an update to the
bzr branch. The branch is now up to mainline state as of the 12th.
Merged 3 4.5 patches into Linaro GCC 4.6. Upstream review isn't
happening, so I've decided to commit them anyway. The last upload (FSF
mainline as of 12th Feb) will therefore become the baseline I'm going to
use for Linaro GCC 4.6.
Begun benchmarking the questionable patches before forward porting them,
using EEMBC. Michael Hope has given me access to one of his A9 Panda
boards in New Zealand. This ought to have been straight-forward, but of
course it wasn't. It took me a while to convince myself I was getting
meaningful results and testing the right thing. Also the A9 seemed to be
able to complete the configured iterations in 'zero' time, which fooled
me for a while. I think I now have a set up that works. It seems to run
very slowly sometimes though - something to do with SSH?
----
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
* ARM EABI half-precision functions
http://gcc.gnu.org/ml/gcc-patches/2011-02/msg00874.html
* ARM Thumb2 Spill Likely tweak
http://gcc.gnu.org/ml/gcc-patches/2011-02/msg00880.html
RAG:
Red:
Amber:
Green: DATE/QEMU conference place confirmed, travel booked
Current Milestones:
| Planned | Estimate | Actual |
qemu-linaro 2011-03 | 2011-03-08 | 2011-03-08 | |
Historical Milestones:
finish virtio-system | 2010-08-27 | postponed | |
finish testing PCI patches | 2010-10-01 | 2010-10-22 | 2010-10-18 |
successful ARM qemu pull req | 2010-12-16 | 2010-12-16 | 2010-12-16 |
finish qemu-cont-integration | 2011-01-25 | 2011-01-25 | handed off |
first qemu-linaro release | 2011-02-08 | 2011-02-08 | 2011-02-08 |
* maintain-beagle-models:
+ implemented missing epoll syscalls for qemu usermode,
submitted upstream
https://bugs.launchpad.net/qemu-linaro/+bug/644961
+ tracked down the problem causing serial console to break:
the new Linux driver uses some extra features of the UART
which we weren't modelling
https://bugs.launchpad.net/qemu-linaro/+bug/714600
* merge-correctness-fixes:
+ reworked VZIP/VUZP patch as per review comments, resubmitted
+ reviewed CL's latest shift patches, added fixes of my own for
large shift counts and overlapping src/dest regs, submitted
a 10 patch rolled up series
+ reviewed a patch for adding cp15 VA-PA translation ops
+ reviewed various versions of vrecpe/vsqrte patches from CL
* versatile-express model:
B Labs kindly made available their Versatile Express board model:
https://github.com/bbalban/qemu/commits/universal-branch
and I've spent a few days getting it to boot a Linaro kernel,
fixing a few bugs and cleaning up the patchset in preparation
for upstreaming it.
This included discovering a bug in qemu's SD card model which
was causing Linux not to be able to detect cards on PL181,
and resulting in spurious qemu warnings on omap3:
https://bugs.launchpad.net/qemu-linaro/+bug/714606
* other:
+ ARM architecture Q&A for modelling engineers
+ booked travel/hotel for QEMU conference
* meetings: toolchain, PDSW-tools, PD comms, Linaro-in-ARM network
infrastructure, pdsw-doughnuts and 1st birthday celebration,
Current qemu patch status is tracked here:
https://wiki.linaro.org/PeterMaydell/QemuPatchStatus
Absences:
17/18 March: QEMU Users Forum, Grenoble
Holiday: 22 Apr - 2 May
9-13 May: UDS, Budapest
(maybe) ~17-19 August: QEMU/KVM strand at LinuxCon NA, Vancouver
Hi,
* continued to look into latrace and found an issue in case a dynamic
library gets unloaded. Otherwise latrace looks quite good on ARM.
https://wiki.linaro.org/KenWerner/Sandbox/latrace
* chasing bugs:
- After a lot of testing Andy Green has made a big step forward in
finding the root cause for the shut-down issue of my PandaBoard.
The PMIC is seeing an overcurrent and issues an interrupt that gets
ignored by current kernels. Then the PMIC shuts the board down for
safety reasons. As a workaround Andy has made a kernel patch for the
twl6030 driver that enables all interrupt sources. The kernel will
acknowledge the overcurrent reported by the PMIC and the board survives.
A patched kernel binary can be found at:
https://wiki.linaro.org/KenWerner/Sandbox/708883
- While testing Andys patches on the linaro natty kernels I ran into
https://bugs.launchpad.net/bugs/720055
- The flash-kernel utility doesn't work on the PandaBoard because the
subarch check expects omap4 instead of omap:
https://bugs.launchpad.net/bugs/721147
- Looked into the apr fail (process shared mutex's fail on armel v7).
Their mutex functionality can be mappped to various methods, but only
pthread is of interest here. The code relies on pthread_mutex_lock and
pthread_mutex_trylock which is implemented by the (e)glibc. The c library
uses GCCs __sync primitives if eglibc >= 2.12.1-0ubuntu11 and GCC >=4.5.
The testprocmutex testcase passes now.
https://bugs.launchpad.net/bugs/604753
Regards
Ken
"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
Sitz der Gesellschaft: Böblingen | Registergericht: Amtsgericht
Stuttgart, HRB 243294
