Your call.
Dan
On 8/20/14 11:05 AM, Christian Tornqvist wrote:
I talked to Staffan Friberg (perf tech lead) about enabling this in a
release builds and this is his opinion:
"For /homeparams I think enable it now in fastdebug, let's use it for a
while and understand home much of a benefit it is for debugging. If it is a
huge help let's consider it for release, but that will require a lot of
performance testing before commiting"
I agree with Staffan and think we should only enable it in fastdebug builds
for now.
Thanks,
Christian
-----Original Message-----
From: Daniel D. Daugherty [mailto:daniel.daughe...@oracle.com]
Sent: Wednesday, August 20, 2014 12:02 PM
To: Christian Tornqvist
Cc: hotspot-...@openjdk.java.net; build-dev@openjdk.java.net
Subject: Re: RFR(S): 8027480 - Build Windows x64 fastdebug builds using
/homeparams
On 8/20/14 9:48 AM, Christian Tornqvist wrote:
indicate that we shouldn't need this change in our debug/fastdebug
builds.
However, you looked at the generated prologue code before and after
turning on this option right?
Our fastdebug builds are compiled with /O2 which doesn't spill the
parameters onto the stack, our debug builds (with /Od) will do this so
passing /homeparams there is a no-op.
Here is a look at the prologue code for
ClassFileParser::parse_constant_pool_entries() before /homeparams:
mov dword ptr [rsp+10h],edx
push rbp
push rsi
and here is with /homeparams:
mov qword ptr [rsp+18h],r8
mov dword ptr [rsp+10h],edx
mov qword ptr [rsp+8],rcx
push rbp
push rsi
Cool. When we did the Full Debug Symbols (FDS) project, one of the things we
did was try to use the same optimization and debug options with
RELEASE/product builds as with fastdebug builds. Since we're generating
debug info for all builds configs, we thought this was a really good design
goal unless we ran into a performance issue.
During the FDS project, we saw no performance change when we switched the
optimization options and included the various generate-debug-info options.
A long way of saying:
I think you should enable /homeparams for RELEASE/product builds.
:-)
Dan
Thanks,
Christian
-----Original Message-----
From: Daniel D. Daugherty [mailto:daniel.daughe...@oracle.com]
Sent: Wednesday, August 20, 2014 11:17 AM
To: Christian Tornqvist
Cc: hotspot-...@openjdk.java.net; build-dev@openjdk.java.net
Subject: Re: RFR(S): 8027480 - Build Windows x64 fastdebug builds
using /homeparams
On 8/20/14 8:49 AM, Christian Tornqvist wrote:
Do we have any idea how much of a change? Do we care? I'm presuming
the
increased debuggability is worth it.
It adds 0-4 additional stack movs in function prologue code which
should have a very low impact, it's only on debug/fastdebug builds.
I missed that this was a non-RELEASE build change in my original review.
These two blurbs from the MSDN note:
> However, by default in a release build, the register parameters >
will not be written to the stack, into the space that is already >
provided for the parameters. This makes it difficult to debug an >
optimized (release) build of your program.
and
> In a debug build, the stack is always populated with parameters >
passed in registers.
indicate that we shouldn't need this change in our debug/fastdebug builds.
However, you looked at the generated prologue code before and after
turning on this option right?
Does this mean that the MSDN note is not correct for the way that we
do debug and fastdebug builds? We might have some option enabled that
prevents the default /homeparams behavior from working...
Dan
The above block will also apply to an "ia64" build. We don't support
that
anymore, but I don't know if any licensees support it.
I've changed the checks in vm.make and WinGammaPlatformVC10.java
Do we need to do anything about the new, but unused platform to
make
lint-like tools not squawk?
I'll open a new bug to clean up the VC7/8/9 files in ProjectCreator.
New webrev:
http://cr.openjdk.java.net/~ctornqvi/webrev/8027480/webrev.01/
Thanks,
Christian
-----Original Message-----
From: Daniel D. Daugherty [mailto:daniel.daughe...@oracle.com]
Sent: Wednesday, August 20, 2014 9:48 AM
To: Christian Tornqvist
Cc: hotspot-...@openjdk.java.net
Subject: Re: RFR(S): 8027480 - Build Windows x64 fastdebug builds
using /homeparams
> http://cr.openjdk.java.net/~ctornqvi/webrev/8027480/webrev.00/
General Comment
The MSDN note says:
> /homeparams does imply a performance disadvantage, because it >
does require a cycle to load the register parameters on to the stack.
Do we have any idea how much of a change? Do we care? I'm presuming
the increased debuggability is worth it.
make/windows/makefiles/vm.make
line 38: !else
line 39: CXX_FLAGS=$(CXX_FLAGS) /D "ASSERT" /homeparams
line 40: !endif
The above block will also apply to an "ia64" build.
We don't support that anymore, but I don't know if
any licensees support it.
src/share/tools/ProjectCreator/BuildConfig.java
No comments.
src/share/tools/ProjectCreator/WinGammaPlatformVC10.java
line 373: if(!platformName.equals("Win32")) {
line 374: addAttr(rv, "AdditionalOptions", "/homeparams");
The above block will also apply to an "ia64" build.
src/share/tools/ProjectCreator/WinGammaPlatformVC7.java
src/share/tools/ProjectCreator/WinGammaPlatformVC8.java
Do we need to do anything about the new, but unused
platform to make lint-like tools not squawk?
Thumbs up.
Dan
On 8/19/14 5:39 PM, Christian Tornqvist wrote:
Hi everyone,
This change adds /homeparams
(http://msdn.microsoft.com/en-us/library/6exwh0y6.aspx) to compiler
flags when building fastdebug on Windows x64. This causes the
compiler to generate code to spill the first 4 arguments to the
stack (they're normally only passed in registers), which should make
it easier
to debug.
I also changed the ProjectCreator to enable building with this using
Visual Studio. The size of jvm.dll increases with about 3% (about
504k
increase).
Verified that it builds correctly using Visual Studio and JPRT, the
generation of the spill code has been verified by comparing prologue
code for several functions in the JVM with/without using /homeparams.
Webrev:
http://cr.openjdk.java.net/~ctornqvi/webrev/8027480/webrev.00/
Bug:
https://bugs.openjdk.java.net/browse/JDK-8027480
Thanks,
Christian
