[webkit-dev] Bring back ARMv6 support to JSC

Tue Sep 5 06:51:31 PDT 2017

I think that JIT support on platforms that don’t get regular tuning doesn’t make sense. I think we should:

- Remove JIT support for 32-bit platforms
- Remove JIT support for Windows
- Remove JSVALUE32_64
- Use cloop In 64-bit mode on 32-bit platforms and Windows. 

I think this approach would be best for the project since it would mean less time spent on JIT ports that are never quite done. 

-Filip

> On Sep 5, 2017, at 6:01 AM, Caio Lima <ticaiolima at gmail.com> wrote:
> 
> Hi guys,I've posted this on the bug thread, but I would also like to
> revive the discussion here.
> 
> After our last discussion, I put some effort to enable IC for ARMv6
> into JIT layers and now I finally collected some results for that.
> 
> Now, we have regressions just into 2 tests in SunSpider (they aren't
> regressing in LongSpider) and 3 into Octane (gbemu, typescript and
> box2d). Also, I see regressions into microbenchmarks, mainly cases
> with observable-side-effects and set/map tests.
> 
> With these results, what do you think about keep working into ARMv6 support?
> 
> Maybe an important report is that I'm almost fixing the errors taking
> the http://trac.webkit.org/changeset/220532 as baseline. Currently
> there are ~40 tests failing, and the majority of them are due to OOM
> into my runtime env, due to memory constraints. I will try to merge it
> with current master this week to check the status of build+failures.
> 
> Regards,
> Caio.
> 
> 2017-08-01 20:52 GMT-03:00 Caio Lima <ticaiolima at gmail.com>:
>> Hi all.
>> 
>> FYI, I keep the last weeks investigating the issue with ARMv6 IC and I
>> was able to find the source of the bug and apply a quick fix to run
>> benchmarks again to get results. I just ran V8Spider, Octane and
>> Kraken by now and I'm attaching the results in this email.
>> 
>> We found some test cases regressing, and my attention now is to
>> identify the reason of the regression and how to fix them. Also, the
>> improvements got with JIT in ARMv6 aren't as big as Filip commented in
>> [1] to supported architectures.
>> 
>> [1] - https://bugs.webkit.org/show_bug.cgi?id=172765#c9
>> 
>> 2017-07-13 19:27 GMT-03:00 Caio Lima <ticaiolima at gmail.com>:
>>> Yes. It probably will take a while to process on device, but I'll run it.
>>> 
>>> Em qui, 13 de jul de 2017 às 17:50, Saam barati <sbarati at apple.com>
>>> escreveu:
>>>> 
>>>> And ARES6.
>>>> 
>>>> - Saam
>>>> 
>>>> 
>>>> On Jul 13, 2017, at 1:50 PM, Saam barati <sbarati at apple.com> wrote:
>>>> 
>>>> Can you please run Octane and Kraken too?
>>>> 
>>>> - Saam
>>>> 
>>>> On Jul 13, 2017, at 7:47 AM, Caio Lima <ticaiolima at gmail.com> wrote:
>>>> 
>>>> Finally I got the results from the last benchmark run. The results
>>>> shows that the speed-ups are considerable comparing with CLoop
>>>> version, since we get faster results in a big number of tests and
>>>> regress in a minor number of scripts. I would like to get feedback
>>>> from you as well, but IMHO enabling JIT for ARMv6 looks a good
>>>> improvement step and the amount of code we are touching in current
>>>> trunk code to make it possible is small.
>>>> 
>>>> The results are attached and I also uploaded them in
>>>> https://bugs.webkit.org/show_bug.cgi?id=172765.
>>>> 
>>>> PS.: Some test cases (bigswitch-indirect-symbol-or-undefined,
>>>> bigswitch-indirect-symbol, bigswitch, etc) are failing now and I'm
>>>> already investigating the source of problem to fix them.
>>>> 
>>>> Regards,
>>>> Caio.
>>>> 
>>>> 2017-07-05 22:54 GMT-03:00 Filip Pizlo <fpizlo at apple.com>:
>>>> 
>>>> To be clear, I’m concerned that the 32-bit JIT backends have such bad
>>>> tuning for these embedded platforms that it’s just pure badness. Until you
>>>> can prove that you can change this, I think that porting should focus on
>>>> making the cloop great. Then, we can rip out support for weird CPUs rather
>>>> than bringing it back.
>>>> 
>>>> -Filip
>>>> 
>>>> On Jul 5, 2017, at 6:14 PM, Caio Lima <ticaiolima at gmail.com> wrote:
>>>> 
>>>> 2017-07-05 18:25 GMT-03:00 Filip Pizlo <fpizlo at apple.com>:
>>>> 
>>>> You need to establish that the JIT is a performance progression over the
>>>> LLInt on ARMv6. I am opposed to more ARMv6 patches landing until there is
>>>> some evidence provided that you’re actually getting speed-ups.
>>>> 
>>>> 
>>>> It makes sense. I can get these numbers related to JIT.
>>>> 
>>>> BTW, there is a Patch that isn't JIT related
>>>> (https://bugs.webkit.org/show_bug.cgi?id=172766).
>>>> 
>>>> Regards,
>>>> Caio.
>>>> 
>>>> -Filip
>>>> 
>>>> On Jun 13, 2017, at 6:48 PM, Caio Lima <ticaiolima at gmail.com> wrote:
>>>> 
>>>> Hi All.
>>>> 
>>>> Some of you guys might know me through the work I have been doing in
>>>> JSC. The experience working with WebKit has been great so far, thank
>>>> you for the reviews!
>>>> 
>>>> Since 1st May, we at Igalia have been working on bring back the ARMv6
>>>> support into JSC. We already have commits into our downstream branch
>>>> port[2] that fixes some compile/runtime errors when building JSC to
>>>> ARMv6 and also fixes some bugs. However, this branch is not synced
>>>> with WebKit upstream tree and I would like to pursue the upstreaming
>>>> of this ARMv6/JSC support to WebKit.
>>>> 
>>>> As a long shot, we are planning to maintain the ARMv6 support and make
>>>> tests run as green as possible. Also, it's our goal make ARMv6 support
>>>> not interfere with other ARM versions support code negatively and we
>>>> will be in charge of implement platform-specific fixes/features for
>>>> JSC/ARM6, this way no imposing burden to the rest of the community.
>>>> 
>>>> To keep track of work to be done, I've create a meta-bug in
>>>> bugzilla[3] and it's going to be used firstly to organize the commits
>>>> from our downstream branch, but pretty soon I'm going to create issues
>>>> related with javascriptcore-test failures and send patches to fix
>>>> them. We have already submitted 3 patches (they are marked as
>>>> dependence of [3]) that fixes ARMv6 into LLInt and JIT layers and got
>>>> a round of review into them.
>>>> 
>>>> Best Regards,
>>>> Caio.
>>>> 
>>>> [1] - https://www.igalia.com/about-us/coding-experience
>>>> [2] - https://github.com/WebPlatformForEmbedded/WPEWebKit
>>>> [3] - https://bugs.webkit.org/show_bug.cgi?id=172765
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>>>> 
>>>> 
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>>> 