Re: [Qemu-devel] [PATCH for-2.8?] rules.mak: speedup save-vars load-vars

[Paolo Bonzini]

On 07/11/2016 13:49, Stefan Hajnoczi wrote:
> On Wed, Nov 02, 2016 at 05:24:01PM +0100, Paolo Bonzini wrote:
>> Unnesting variables spends a lot of time parsing and executing foreach
>> and if functions.  Because actually very few variables have to be
>> saved and restored, a good strategy is to remember what has to be done
>> in load-vars, and only iterate the right variables in load-vars.
>> For save-vars, unroll the foreach loop to provide another small
>> improvement.
>>
>> This speeds up a "noop" build from around 15.5 seconds on my laptop
>> to 11.7 (25% roughly).
>>
>> Signed-off-by: Paolo Bonzini <address@hidden>
>> ---
>>      I'm wondering if this would be acceptable for 2.8.
>>      I also have sent patches to GNU make that save another
>>      20%, down to 9.8 seconds.
> 
> Sorry but I'd like to stick to the soft freeze policy.  This patch is a
> nice improvement but it's not a bug fix.  Let's merge it for 2.9.

Fine by me, thanks!

Paolo

>>  rules.mak | 22 ++++++++++------------
>>  1 file changed, 10 insertions(+), 12 deletions(-)
>>
>> diff --git a/rules.mak b/rules.mak
>> index 0333ae3..c0777d7 100644
>> --- a/rules.mak
>> +++ b/rules.mak
>> @@ -192,15 +192,15 @@ clean: clean-timestamp
>>  # save-vars
>>  # Usage: $(call save-vars, vars)
>>  # Save each variable $v in $vars as save-vars-$v, save their object's
>> -# variables, then clear $v.
>> +# variables, then clear $v.  saved-vars-$v caches the list of variables
>> +# that were saved for the objects, in order to speedup load-vars.
>>  define save-vars
>>      $(foreach v,$1,
>>          $(eval save-vars-$v := $(value $v))
>> -        $(foreach o,$($v),
>> -            $(foreach k,cflags libs objs,
>> -                $(if $($o-$k),
>> -                    $(eval save-vars-$o-$k := $($o-$k))
>> -                    $(eval $o-$k := ))))
>> +        $(eval saved-vars-$v := $(foreach o,$($v), \
>> +            $(if $($o-cflags), $o-cflags $(eval save-vars-$o-cflags := 
>> $($o-cflags))$(eval $o-cflags := )) \
>> +            $(if $($o-libs), $o-libs $(eval save-vars-$o-libs := 
>> $($o-libs))$(eval $o-libs := )) \
>> +            $(if $($o-objs), $o-objs $(eval save-vars-$o-objs := 
>> $($o-objs))$(eval $o-objs := ))))
>>          $(eval $v := ))
>>  endef
>>  
>> @@ -213,12 +213,10 @@ define load-vars
>>      $(eval $2-new-value := $(value $2))
>>      $(foreach v,$1,
>>          $(eval $v := $(value save-vars-$v))
>> -        $(foreach o,$($v),
>> -            $(foreach k,cflags libs objs,
>> -                $(if $(save-vars-$o-$k),
>> -                    $(eval $o-$k := $(save-vars-$o-$k))
>> -                    $(eval save-vars-$o-$k := ))))
>> -        $(eval save-vars-$v := ))
>> +        $(foreach o,$(saved-vars-$v),
>> +            $(eval $o := $(save-vars-$o)) $(eval save-vars-$o := ))
>> +        $(eval save-vars-$v := )
>> +        $(eval saved-vars-$v := ))
>>      $(eval $2 := $(value $2) $($2-new-value))
>>  endef
>>  
>> -- 
>> 2.7.4
>>
>>