Re: [dpdk-dev] [PATCH] rte_delay_us can be replaced with user function

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2016-09-22 08:37, Jozef Martiniak -X:
> Hello Thomas,
> 
> > First a general comment: please check your patch with scripts/checkpatches.sh.
> Done. checkpath.pl is taken from latest linux kernel...

I can see these warnings:
UNSPECIFIED_INT: Prefer 'unsigned int' to bare use of 'unsigned'
LEADING_SPACE: please, no spaces at the start of a line

> > What will happen if we need to provide more builtin handlers?
> > I still think that rte_delay_us_block can be exported and initialized
> The idea was to make this function simple&&fast as possible. If user needs
> more builtin handlers - he can implement this functionality within his delay 
> function.
> 
> Btw there is also another patch with the same functionality (uses weak symbols) 
> which I would prefer:
> https://git.fd.io/cgit/vpp/tree/dpdk/dpdk-16.04_patches/0005-Allow-applications-to-override-rte_delay_us.patch

I don't like the VPP patch because it is hacky and weak symbols should
be avoided for static linking.

> Do you have any idea how should rte_delay_us_callback_register look like for 
> multiple handlers ?

Yes, just as simple as an assignment:
void rte_delay_us_callback_register(void (*func)(unsigned))
{
    rte_delay_us = func;
}

We just need to export rte_delay_us_block and call
rte_delay_us_callback_register(rte_delay_us_block)
at EAL initialization or in a constructor.


> Other comments are accepted.
> 
> Best regards,
> Jozef
> 
> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com] 
> Sent: Wednesday, September 21, 2016 3:13 PM
> To: Jozef Martiniak -X (jozmarti - PANTHEON TECHNOLOGIES at Cisco) <jozmarti@cisco.com>
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] rte_delay_us can be replaced with user function
> 
> Hi,
> 
> I think this feature should enter in the release 16.11.
> We just need to make sure it is implemented with the right API.
> Do you have any comment about managing several builtin handlers?
> 
> 
> 2016-09-13 22:04, Thomas Monjalon:
> > Hi,
> > 
> > Sorry for late review.
> > This patch was in a summer hole :/
> > 
> > First a general comment: please check your patch with 
> > scripts/checkpatches.sh.
> > In order to ease tracking of this patch, please increment the version 
> > when sending a new one in the same thread:
> > 	git send-email -1 -v3 --annotate --to dev@dpdk.org \
> > 	--in-reply-to 1469016644-6521-1-git-send-email-jozmarti@cisco.com
> > 
> > More comments below.
> > 
> > 2016-07-20 14:10, jozmarti@cisco.com:
> > > +void rte_delay_us_callback_register(void (*userfunc)(unsigned)) {
> > > +    if (userfunc == NULL)
> > > +        rte_delay_us = rte_delay_us_block;
> > 
> > Here you are creating an exception for rte_delay_us_block which is 
> > mapped as a NULL handler.
> > What will happen if we need to provide more builtin handlers?
> > I still think that rte_delay_us_block can be exported and initialized 
> > as the default handler. Other opinions are obviously welcome.
> > 
> > > +    else
> > > +        rte_delay_us = userfunc;
> > > +}
> > > +
> > > +static void __attribute__((constructor))
> > > +rte_timer_init(void)
> > > +{
> > > +    /* set rte_delay_us_block as a delay function */
> > > +    rte_delay_us_callback_register(NULL);
> > > +}
> > > diff --git a/lib/librte_eal/common/include/generic/rte_cycles.h 
> > > b/lib/librte_eal/common/include/generic/rte_cycles.h
> > > index 8cc21f2..7a45b58 100644
> > > --- a/lib/librte_eal/common/include/generic/rte_cycles.h
> > > +++ b/lib/librte_eal/common/include/generic/rte_cycles.h
> > > @@ -182,13 +182,16 @@ rte_get_timer_hz(void)  }
> > >  
> > >  /**
> > > + *
> > 
> > useless newline
> > 
> > >   * Wait at least us microseconds.
> > > + * This function can be replaced with user-defined function using
> > > + * rte_delay_us_callback_register
> > 
> > I think you can use @see to point to rte_delay_us_callback_register.
> > 
> > >   *
> > >   * @param us
> > >   *   The number of microseconds to wait.
> > >   */
> > >  void
> > > -rte_delay_us(unsigned us);
> > > +(*rte_delay_us)(unsigned us);
> > >  
> > >  /**
> > >   * Wait at least ms milliseconds.
> > > @@ -202,4 +205,14 @@ rte_delay_ms(unsigned ms)
> > >  	rte_delay_us(ms * 1000);
> > >  }
> > >  
> > > +/**
> > > + * Replace rte_delay_us with user defined function.
> > > + *
> > > + * @param userfunc
> > > + *   User function which replaces rte_delay_us. NULL restores
> > > + *   buildin block delay function.
> > 
> > buildin -> builtin ?
> > 
> > > + */
> > > +void rte_delay_us_callback_register(void(*userfunc)(unsigned));
> > 
> 
>