[RFT - PATCH v2 0/2] KVM/arm64: add fp/simd lazy switch support

Mario Smarduch m.smarduch at samsung.com
Mon Oct 12 09:29:23 PDT 2015

Hi Christoffer, Marc -
  I just threw this test your way without any explanation.

The test loops, does fp arithmetic and checks the truncated result.
It could be a little more dynamic have an initial run to
get the sum to compare against while looping, different fp
hardware may come up with a different sum, but truncation is
to 5'th decimal point.

The rationale is that if there is any fp/simd corruption
one of these runs should fail. I think most likely scenario
for that is a world switch in midst of fp operation. I've
instrumented (basically add some tracing to vcpu_put()) and
validated vcpu_put gets called thousands of time (for v7,v8)
for an over night test running two guests/host crunching
fp operations.

Other then that not sure how to really catch any problems
with the patches applied. Obviously this is a huge issues, if this has
any problems. If you or Marc have any other ideas I'd be happy
to enhance the test.


On 10/5/2015 8:45 AM, Christoffer Dall wrote:
> On Tue, Sep 22, 2015 at 04:34:01PM -0700, Mario Smarduch wrote:
>> This is a 2nd itteration for arm64, v1 patches were posted by mistake from an 
>> older branch which included several bugs. Hopefully didn't waste too much of 
>> anyones time.
>> This patch series is a followup to the armv7 fp/simd lazy switch
>> implementation, uses similar approach and depends on the series - see
>> https://lists.cs.columbia.edu/pipermail/kvmarm/2015-September/016516.html
>> It's based on earlier arm64 fp/simd optimization work - see
>> https://lists.cs.columbia.edu/pipermail/kvmarm/2015-July/015748.html
>> And subsequent fixes by Marc and Christoffer at KVM Forum hackathon to handle
>> 32-bit guest on 64 bit host (and may require more here) - see
>> https://lists.cs.columbia.edu/pipermail/kvmarm/2015-August/016128.html
>> This series has be tested with arm64 on arm64 with several FP applications 
>> running on host and guest, with substantial decrease on number of 
>> fp/simd context switches. From about 30% down to 2% with one guest running.
>> At this time I don't have arm32/arm64 working and hoping Christoffer and/or
>> Marc (or anyone) can test 32-bit guest/64-bit host.
> Did you already have some test infrastructure/applications that I can
> reuse for this purpose or do I have to write userspace software?
> -Christoffer

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