[PING] RFR(M): 8207343: Automate vtable/itable stub size calculation
Schmidt, Lutz
lutz.schmidt at sap.com
Tue Aug 14 07:46:17 UTC 2018
Hi Vladimir,
the answer is simple: No, I did not. The proposed change is basically a generalized, harmonized variant of a modification we have been using at SAP for many years.
Your idea is interesting, though. I (still) do not completely like the implementation currently in RFR. The code size variance caused by data only known at runtime (constants, offsets, for example) makes the generators ugly.
Using a temp buffer adds other complexities. What about relocations, for example. Without having had a deeper look, I expect the effort to be "considerable".
Thanks,
Lutz
On 14.08.18, 00:49, "Vladimir Kozlov" <vladimir.kozlov at oracle.com> wrote:
Hi Lutz,
Did you consider to generate these stubs in temp buffer before publishing them in CodeCache as we do
for nmethods?
Thanks,
Vladimir
On 8/13/18 3:52 AM, Schmidt, Lutz wrote:
> Dear Community,
> are there any praises, objections, questions, comments, or even reviews for this change?
> Thanks for considering!
> Lutz
>
> On 13.08.18, 12:47, "Schmidt, Lutz" <lutz.schmidt at sap.com> wrote:
>
> Hi Boris,
>
> back from vacation I'd like to elaborate a bit more on your comments.
>
> Based on your input, I have changed the description in VtableStub::pd_code_alignment() to read
> "ARM32 cache line size is not an architected constant. We just align on word size."
>
> The description for aarch64 was adapted accordingly:
> "aarch64 cache line size is not an architected constant. We just align on 4 bytes (instruction size)."
>
> With respect to the variable name, I just harmonized the naming across all platforms. I would appreciate if you could live with it. Another option would be to just return a value, without using any variable name. I don't like that too much, but if the community prefers it...
>
> I have updated http://cr.openjdk.java.net/~lucy/webrevs/8207343.01 in-place with just the two comment lines modified.
>
> Thank you,
> Lutz
>
> On 07.08.18, 22:12, "Schmidt, Lutz" <lutz.schmidt at sap.com> wrote:
>
> Hi Boris,
> thanks for looking at this. I will respond to your comments in more detail next week. I'm on vacation this week.
> Thanks,
> Lutz
>
> On 05.08.18, 19:08, "Boris Ulasevich" <boris.ulasevich at bell-sw.com> wrote:
>
> Hi Lutz,
>
> I have run jtreg with your change and do not see new fails (test that
> fails on aarch64 is excluded for 32 bit platforms).
>
> I am OK with your change (I'm not a reviewer). But description and
> variable name in VtableStub::pd_code_alignment function looks strange
> for me. Raspberry Pi2 ARM1176JZF-S processor has a cache line length of
> 32 bytes, and, as I know, icache line size is not a constant for ARM32
> architecture.
>
> regards,
> Boris
>
> On 02.08.2018 15:02, Schmidt, Lutz wrote:
> > Hi Zhongwei,
> >
> > thank you for testing aarch64. Given my lack of expertise, I am surprised there are only those two issues.
> > Ad 1.: fixed. The declaration just a few lines above was forgotten to adapt.
> > Ad 2.: adapted. I pushed the estimate to 152 bytes. I expected this value would require some adjustment.
> >
> > Please find a new webrev with the changes at http://cr.openjdk.java.net/~lucy/webrevs/8207343.01
> >
> > Best Regards,
> > Lutz
> >
> > On 02.08.18, 04:45, "Zhongwei Yao" <Zhongwei.Yao at arm.com> wrote:
> >
> > Hi, Lutz,
> >
> > I have tested it on aarch64 by running jtreg tests. And find two tiny issues in vtableStubs_aarch64.cpp's VtableStubs::create_itable_stub function:
> > 1. typecheckSize on line 212 is not defined.
> > 2. estimate on line 211 is not large enough, I get 148 in gc/g1/TestFromCardCacheIndex.java case. Here is the assertion failure from that case:
> > assert(slop_delta >= 0) failed: itable #3: Code size estimate (140) for lookup_interface_method too small, required: 148
> >
> > However, I don't have tested the modification in vtableStubs_arm.cpp due to I don't have an arm32 environment at hand.
> >
> > --
> > Best regards,
> > Zhongwei
> >
> > ________________________________________
> > From: hotspot-compiler-dev <hotspot-compiler-dev-bounces at openjdk.java.net> on behalf of Schmidt, Lutz <lutz.schmidt at sap.com>
> > Sent: Monday, July 30, 2018 3:57:05 PM
> > To: hotspot-compiler-dev at openjdk.java.net
> > Subject: RFR(M): 8207343: Automate vtable/itable stub size calculation
> >
> > Dear all,
> >
> > may I please request reviews for this change:
> >
> > Bug: https://bugs.openjdk.java.net/browse/JDK-8207343
> > Webrev: http://cr.openjdk.java.net/~lucy/webrevs/8207343.00/
> >
> > With this change, I try to get rid of the a-priory size guessing for vtable and itable stubs. Please refer to the bug description for all the details. I didn't want to duplicate that text.
> >
> > ARM and AARCH64 help requested!
> > The edits in vtableStubs_aarch64.cpp and vtableStubs_arm.cpp are made blindfolded. I am neither an ARM expert nor do I have build or test hardware available. I would be very grateful if one of the ARM gurus could please fill in for me.
> >
> > Thank you!
> > Lutz
> >
> >
> >
> >
>
>
>
>
>
>
More information about the hotspot-compiler-dev
mailing list