Re: [Qemu-devel] [PATCH] Only build with -g CFLAGS/LDFLAGS if using --enable-debug and add --optflags.

[Blue Swirl]

On Wed, Sep 7, 2011 at 10:54 AM, Juan Quintela <address@hidden> wrote:
> Brad <address@hidden> wrote:
>> ----- Original message -----
>>> On 09/06/11 10:02, Brad wrote:
>>> > Only build with -g CFLAGS/LDFLAGS if using --enable-debug.
>>> > Add --optflags to allow overriding the default optimization
>>> > level added to CFLAGS.
>>> >
>>> > This is a first draft of coming up with a patch I could potentially
>>> > push upstream based on much cruder local patches to do something
>>> > similar. I'm trying to eliminate having to patch the configure
>>> > script.
>>>
>>> You don't have to.   You can just run 'make CFLAGS="$optflags"' to
>>> override the defaults.   Nevertheless having optflags would be nice as
>>> you don't have to type this for each make run then.
>>
>> I do when its unconditionally on the commandline either way. If the 
>> configure scipt didnt put it their if CFLAGS wasnt empty it wouldnt be an 
>> issue.
>
>        $(call quiet-command,$(CC) $(QEMU_INCLUDES) $(QEMU_CFLAGS) 
> $(QEMU_DGFLAGS) $(CFLAGS) -c -o $@ $<,"  CC    $(TARGET_DIR)$@")
>
> this is the rule called in rules.make.  QEMU don't use CFLAGS
> internally^W^W^W^W, it is only used for -g -O2, so it should be enough
> to use make CFLAGS="" or something like that.
>
>>
>>> I don't think we should mess with the -g flag.   It should stay enabled
>>> by default, so you can easily get a useful stacktrace out of a core
>>> without having to rebuild with debug info first.
>>
>> I dont care what the default is as long as I can disable it without patching.
>
> What is the reason for that?  I guess that compilation speed/memory, but
> just to be sure.

Also disk space. Speed/memory effect seems to be about 3%.

Generating sparc64-softmmu/translate.o with -g, time -v output:
        User time (seconds): 33.00
        System time (seconds): 0.95
        Percent of CPU this job got: 99%
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:34.01
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Maximum resident set size (kbytes): 1636016
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 0
        Minor (reclaiming a frame) page faults: 240264
        Voluntary context switches: 7
        Involuntary context switches: 3201
        Swaps: 0
        File system inputs: 0
        File system outputs: 17488
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0
        Page size (bytes): 4096
        Exit status: 0
$ ls -sh translate.o
2.5M translate.o

Without:
        User time (seconds): 31.55
        System time (seconds): 1.10
        Percent of CPU this job got: 99%
        Elapsed (wall clock) time (h:mm:ss or m:ss): 0:32.73
        Average shared text size (kbytes): 0
        Average unshared data size (kbytes): 0
        Average stack size (kbytes): 0
        Average total size (kbytes): 0
        Maximum resident set size (kbytes): 1619056
        Average resident set size (kbytes): 0
        Major (requiring I/O) page faults: 0
        Minor (reclaiming a frame) page faults: 220316
        Voluntary context switches: 7
        Involuntary context switches: 3335
        Swaps: 0
        File system inputs: 0
        File system outputs: 4040
        Socket messages sent: 0
        Socket messages received: 0
        Signals delivered: 0
        Page size (bytes): 4096
        Exit status: 0
$ ls -sh translate.o
768K translate.o