[PATCH] D16726: [Profiling] Speed up unittests by ~5x

Mon Feb 8 16:42:44 PST 2016

On Mon, Feb 8, 2016 at 4:38 PM, David Blaikie via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

>
>
> On Mon, Feb 8, 2016 at 4:25 PM, Xinliang David Li <davidxl at google.com>
> wrote:
>
>> On Mon, Feb 8, 2016 at 4:12 PM, David Blaikie <dblaikie at gmail.com> wrote:
>> >
>> >
>> > On Mon, Feb 8, 2016 at 4:00 PM, Xinliang David Li <davidxl at google.com>
>> > wrote:
>> >>
>> >> Yes, if we talk about all tests in different repos collectively, 0 is
>> >> probably covered -- but that is still an assumption from the
>> >> unittest's point of view.
>> >
>> >
>> > Ah, sure - I agree it (along with any other API surface area) should be
>> > covered by a unit test, even if the codepath is also covered by a higher
>> > level test of some kind.
>> >
>> > But it looks like the 0 padding case is covered by other /unit/ tests
>> in the
>> > same file.
>>
>> AFAIK, this is the only unittest that covers 0 padding case.
>>
>
> Presumably any other test testing InstrProfSymtab::create tests the zero
> padding case, so far as I'm understanding?
> (instr_prof_symtab_test, instr_prof_symtab_module_test?)
>
> (also, as I look at this - the tests seem generally pretty repetitive and
> brittle - repeating the same string in many places, for example & seem
> overly verbose, testing several more inputs than seem
> necessary/constructive (instr_prof_symtab_test tests 5 strings - why not
> one or two? instr_prof_symtab_module_test tests even more... - no tests
> seem to test a failed lookup (getFuncName with a hash that is not present))
>
>
No -- those tests do not test serialization nor testing combining two
serial segments together which is tested here (simulating what linker does).

> It looks like this could be simplified across the board & make it clearer
> what's being tested and how it's covering all the functionality of the
> InstrProfRecord class.
>
>
>>
>> > This seems like a reasonable case of test case reduction by
>> > combination (if you have {a, b} x {x, y} to test you can test it in two
>> > cases {a, x}, {b, y} rather than running 4 tests, since the features are
>> > independent).
>>
>> We need to be very careful about reducing {a,b}x{x,y} into {a,x} and
>> {b,y} though -- it makes explicit assumption about the implementation
>> -- there might be subtle dependencies there..
>>
>
> Agreed, though it is impractical to assume everything's related to
> everything else - testing would be prohibitive. So we generally test fairly
> precisely/narrowly within the regression suite, and leave it to integration
> tests (like the test-suite, self hosts, etc) to test more broadly for the
> cross-functional interactions.
>
> That's not to say that some tests don't end up a bit redundant so as to
> get more explicit coverage.
>

yes -- that is why I said 'we need to be careful' -- one of the biggest
pitfalls of writing tests is making assumptions above coverage.  In lack of
strong proof, I would err on the more conservative side.

David

>
> - David
>
>
>>
>> David
>>
>> >
>> >>
>> >>
>> >> David
>> >>
>> >> On Mon, Feb 8, 2016 at 3:55 PM, David Blaikie <dblaikie at gmail.com>
>> wrote:
>> >> >
>> >> >
>> >> > On Mon, Feb 8, 2016 at 3:53 PM, Xinliang David Li <
>> davidxl at google.com>
>> >> > wrote:
>> >> >>
>> >> >> On Mon, Feb 8, 2016 at 3:30 PM, David Blaikie <dblaikie at gmail.com>
>> >> >> wrote:
>> >> >> >
>> >> >> >
>> >> >> > On Mon, Feb 8, 2016 at 3:17 PM, Xinliang David Li
>> >> >> > <davidxl at google.com>
>> >> >> > wrote:
>> >> >> >>
>> >> >> >> On Mon, Feb 8, 2016 at 3:12 PM, David Blaikie <
>> dblaikie at gmail.com>
>> >> >> >> wrote:
>> >> >> >> >
>> >> >> >> >
>> >> >> >> > On Mon, Feb 8, 2016 at 3:08 PM, Xinliang David Li
>> >> >> >> > <davidxl at google.com>
>> >> >> >> > wrote:
>> >> >> >> >>
>> >> >> >> >> On Mon, Feb 1, 2016 at 10:44 AM, David Blaikie
>> >> >> >> >> <dblaikie at gmail.com>
>> >> >> >> >> wrote:
>> >> >> >> >> >
>> >> >> >> >> >
>> >> >> >> >> > On Fri, Jan 29, 2016 at 5:58 PM, Xinliang David Li
>> >> >> >> >> > <davidxl at google.com>
>> >> >> >> >> > wrote:
>> >> >> >> >> >>
>> >> >> >> >> >> To clarify, it is not 128 iterations, but creating a symbol
>> >> >> >> >> >> table
>> >> >> >> >> >> with
>> >> >> >> >> >> 128 entries -- which is a reasonable size.
>> >> >> >> >> >
>> >> >> >> >> >
>> >> >> >> >> > We don't generally test on "realistic" sized inputs in the
>> >> >> >> >> > regression
>> >> >> >> >> > suite.
>> >> >> >> >> > We write targeted tests for functionality. Broad testing is
>> >> >> >> >> > done
>> >> >> >> >> > in
>> >> >> >> >> > the
>> >> >> >> >> > test-suite and other integration level testing.
>> >> >> >> >> >
>> >> >> >> >> >>
>> >> >> >> >> >> Test coverage wise, it is probably the same as a 3-entry
>> >> >> >> >> >> symtab.
>> >> >> >> >> >
>> >> >> >> >> >
>> >> >> >> >> > Then let's use a 3-entry symtab.
>> >> >> >> >> >
>> >> >> >> >> > (why 3? Because it tests the boundaries (first and last) and
>> >> >> >> >> > one
>> >> >> >> >> > "normal"
>> >> >> >> >> > case of a non-boundary value - while the boundaries probably
>> >> >> >> >> > aren't
>> >> >> >> >> > interesting in this algorithm, it's cheap enough to just
>> follow
>> >> >> >> >> > that
>> >> >> >> >> > common
>> >> >> >> >> > practice in test case design)
>> >> >> >> >>
>> >> >> >> >> Will update it to 3.
>> >> >> >> >>
>> >> >> >> >> >
>> >> >> >> >> > I'm also curious about the padding parameter - what does it
>> do?
>> >> >> >> >> > Choose
>> >> >> >> >> > how
>> >> >> >> >> > many null characters go between each value? What effect does
>> >> >> >> >> > that
>> >> >> >> >> > have/why
>> >> >> >> >> > is that a tuning parameter? (understanding what it's for can
>> >> >> >> >> > help
>> >> >> >> >> > us
>> >> >> >> >> > choose
>> >> >> >> >> > appropriate test cases/coverage for that functionality)
>> >> >> >> >>
>> >> >> >> >> Internal padding bytes (for alignment to 4 bytes) can be zero
>> to
>> >> >> >> >> 3.
>> >> >> >> >
>> >> >> >> >
>> >> >> >> > Any idea what's particularly useful to test here? (does it just
>> >> >> >> > assert
>> >> >> >> > that
>> >> >> >> > the parameter is [0,3] ? Or does it have well defined behavior
>> >> >> >> > (returning an
>> >> >> >> > error code? doing something else?) outside that range? is any
>> case
>> >> >> >> > more
>> >> >> >> > interesting than any other - or just a simple loop for
>> [0,Padding]
>> >> >> >> > done
>> >> >> >> > at
>> >> >> >> > some point in the algorithm? Does anything test that the
>> algorithm
>> >> >> >> > emitted
>> >> >> >> > the right padding?)
>> >> >> >>
>> >> >> >> It tests that the reader is (flexible) and capable of handing
>> >> >> >> padding
>> >> >> >> bytes not produced by the writer.  How many paddings should be
>> >> >> >> emitted
>> >> >> >> is not specified. For instance, if some producer forces 8 byte
>> >> >> >> alignment, it should be handled too.
>> >> >> >
>> >> >> >
>> >> >> > Ah, OK - perhaps we could just test one pseudo-random (if it's
>> really
>> >> >> > just a
>> >> >> > "while (null byte)" loop to ignore the padding - I'd probably
>> pick 2
>> >> >> > bytes
>> >> >> > of padding, but don't mind any small number) amount of padding to
>> >> >> > test
>> >> >> > that
>> >> >> > the reader ignores it, rather than testing several amounts of
>> >> >> > padding?
>> >> >> > Alternatively/in addition, might be good to test these features
>> >> >> > separately
>> >> >> > to make triage easier? Rather than combining compression and
>> padding
>> >> >> > together - unless there's an interesting interaction between the
>> two
>> >> >> > features in the implementation?
>> >> >> >
>> >> >>
>> >> >> I think 0 is more special here, so I would pick 0 and 1 byte.
>> >> >
>> >> >
>> >> > Is zero bytes of padding not already covered by any other tests? (I
>> >> > assume
>> >> > it's covered by most tests as it sounds like it's the common case?)
>> >> >
>> >> >>
>> >> >> > You say "padding bytes not produced by the writer" - does the
>> writer
>> >> >> > produce
>> >> >> > zero bytes of padding, or some amount of padding that's just not
>> the
>> >> >> > same
>> >> >> > amounts as are being tested here?
>> >> >>
>> >> >> The writer can produce 0 or more padding bytes, the assembler and
>> >> >> linker may or may not pad more. The purpose of the testing is that
>> the
>> >> >> reader does not depend/care about those behavior.
>> >> >>
>> >> >> David
>> >> >>
>> >> >> >
>> >> >> > - David
>> >> >
>> >> >
>> >
>> >
>>
>
>
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