llvm dev - Jun 2017 - My experience using -DLLVM_BUILD_INSTRUMENTED_COVERAGE to generate coverage

On 6/27/2017 1:47 PM, Xinliang David Li wrote:
>
>
> On Mon, Jun 26, 2017 at 7:24 PM, Friedman, Eli 
> <efriedma at codeaurora.org <mailto:efriedma at
codeaurora.org>> wrote:
>
>     On 6/19/2017 7:29 PM, Vedant Kumar wrote:
>>
>>>>     We can reduce testing time by *not* instrumented basic
tools
>>>>     like count, not, FileCheck etc. I filed: llvm.org/PR33501
>>>>     <http://llvm.org/PR33501>.
>>>>
>>>>>     3. The generated profile information takes up a lot of
space:
>>>>>     llc generates a 90MB profraw file.
>>>>
>>>>     I don't have any ideas about how to fix this. You can
decrease
>>>>     the space overhead for raw profiles by altering
>>>>     LLVM_PROFILE_MERGE_POOL_SIZE from 4 to a lower value.
>>>
>>>     Disk space is cheap, but the I/O takes a long time.  I guess
>>>     it's specifically bad for LLVM's "make
check", maybe not so bad
>>>     for other cases.
>>
>>     You can speed up "make check" a bit by using
non-instrumented
>>     versions of count, not, FileCheck, etc.
>
>     I tried looking into this a bit more.  It looks like the profile
>     data file generated by llc contains approximately 5MB of counters
>     (__llvm_prf_cnts), 10MB of "data" (__llvm_prf_data), and 70MB
of
>     __llvm_prf_names. __llvm_prf_data and __llvm_prf_names contain
>     which can be read from the original binary, as far as I can tell.
>     The 80MB of data wouldn't be a big deal if it were just sitting on
>     disk... but we also erase the whole file and rewrite it from
>     scratch after we merge profile counters.
>
>
> Can you check if name compression is turned on in your build?
>
> David
>
I think it is. At least, I didn't intentionally turn it off, and 
examining the file with objdump I don't see any uncompressed strings.  
Not sure if there's any easy way to confirm that.

-Eli

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
Foundation Collaborative Project

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On Tue, Jun 27, 2017 at 2:09 PM, Friedman, Eli <efriedma at
codeaurora.org>
wrote:
> On 6/27/2017 1:47 PM, Xinliang David Li wrote:
>
>
>
> On Mon, Jun 26, 2017 at 7:24 PM, Friedman, Eli <efriedma at
codeaurora.org>
> wrote:
>
>> On 6/19/2017 7:29 PM, Vedant Kumar wrote:
>>
>>
>> We can reduce testing time by *not* instrumented basic tools like
count,
>> not, FileCheck etc. I filed: llvm.org/PR33501.
>>
>> 3. The generated profile information takes up a lot of space: llc
>> generates a 90MB profraw file.
>>
>>
>> I don't have any ideas about how to fix this. You can decrease the
space
>> overhead for raw profiles by altering LLVM_PROFILE_MERGE_POOL_SIZE from
>> 4 to a lower value.
>>
>>
>> Disk space is cheap, but the I/O takes a long time.  I guess it's
>> specifically bad for LLVM's "make check", maybe not so
bad for other cases.
>>
>>
>> You can speed up "make check" a bit by using non-instrumented
versions of
>> count, not, FileCheck, etc.
>>
>>
>> I tried looking into this a bit more.  It looks like the profile data
>> file generated by llc contains approximately 5MB of counters
>> (__llvm_prf_cnts), 10MB of "data" (__llvm_prf_data), and 70MB
of
>> __llvm_prf_names.  __llvm_prf_data and __llvm_prf_names contain which
can
>> be read from the original binary, as far as I can tell.  The 80MB of
data
>> wouldn't be a big deal if it were just sitting on disk... but we
also erase
>> the whole file and rewrite it from scratch after we merge profile
counters.
>>
>>
> Can you check if name compression is turned on in your build?
>
> David
>
>
> I think it is. At least, I didn't intentionally turn it off, and
examining
> the file with objdump I don't see any uncompressed strings.  Not sure
if
> there's any easy way to confirm that.
>

Just a little surprised at the size of __llvm_prf_names section. The llc I
built with IR PGO has a __llvm_prf_names section with size  ~1.4MB.    I
expect FE instrumentation to produce larger name section size, but not so
much bigger.

David
>
> -Eli
>
> --
> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
Foundation Collaborative Project
>
>
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I had an old build of llc with FE instrumentation, the name section size is
about 5MB.  Using coverage is likely to cause the name section to be larger
as there are more references to dead/unused function names.

What do you see when

readelf --string-dump=__llvm_prf_names llc

David

On Tue, Jun 27, 2017 at 2:23 PM, Xinliang David Li <davidxl at google.com>
wrote:
>
>
> On Tue, Jun 27, 2017 at 2:09 PM, Friedman, Eli <efriedma at
codeaurora.org>
> wrote:
>
>> On 6/27/2017 1:47 PM, Xinliang David Li wrote:
>>
>>
>>
>> On Mon, Jun 26, 2017 at 7:24 PM, Friedman, Eli <efriedma at
codeaurora.org>
>> wrote:
>>
>>> On 6/19/2017 7:29 PM, Vedant Kumar wrote:
>>>
>>>
>>> We can reduce testing time by *not* instrumented basic tools like
count,
>>> not, FileCheck etc. I filed: llvm.org/PR33501.
>>>
>>> 3. The generated profile information takes up a lot of space: llc
>>> generates a 90MB profraw file.
>>>
>>>
>>> I don't have any ideas about how to fix this. You can decrease
the space
>>> overhead for raw profiles by altering LLVM_PROFILE_MERGE_POOL_SIZE
from
>>> 4 to a lower value.
>>>
>>>
>>> Disk space is cheap, but the I/O takes a long time.  I guess
it's
>>> specifically bad for LLVM's "make check", maybe not
so bad for other cases.
>>>
>>>
>>> You can speed up "make check" a bit by using
non-instrumented versions
>>> of count, not, FileCheck, etc.
>>>
>>>
>>> I tried looking into this a bit more.  It looks like the profile
data
>>> file generated by llc contains approximately 5MB of counters
>>> (__llvm_prf_cnts), 10MB of "data" (__llvm_prf_data), and
70MB of
>>> __llvm_prf_names.  __llvm_prf_data and __llvm_prf_names contain
which can
>>> be read from the original binary, as far as I can tell.  The 80MB
of data
>>> wouldn't be a big deal if it were just sitting on disk... but
we also erase
>>> the whole file and rewrite it from scratch after we merge profile
counters.
>>>
>>>
>> Can you check if name compression is turned on in your build?
>>
>> David
>>
>>
>> I think it is. At least, I didn't intentionally turn it off, and
>> examining the file with objdump I don't see any uncompressed
strings.  Not
>> sure if there's any easy way to confirm that.
>>
>
>
> Just a little surprised at the size of __llvm_prf_names section. The llc I
> built with IR PGO has a __llvm_prf_names section with size  ~1.4MB.    I
> expect FE instrumentation to produce larger name section size, but not so
> much bigger.
>
> David
>
>>
>> -Eli
>>
>> --
>> Employee of Qualcomm Innovation Center, Inc.
>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
Linux Foundation Collaborative Project
>>
>>
>
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