Re: [patch net-next v4 3/9] devlink: send notifications only if there are listeners

[Jiri Pirko <jiri@resnulli.us>]

Mon, Nov 27, 2023 at 04:00:42PM CET, pabeni@redhat.com wrote:
>On Mon, 2023-11-27 at 13:04 +0100, Jiri Pirko wrote:
>> Mon, Nov 27, 2023 at 12:01:10PM CET, pabeni@redhat.com wrote:
>> > On Thu, 2023-11-23 at 19:15 +0100, Jiri Pirko wrote:
>> > > From: Jiri Pirko <jiri@nvidia.com>
>> > > 
>> > > Introduce devlink_nl_notify_need() helper and using it to check at the
>> > > beginning of notification functions to avoid overhead of composing
>> > > notification messages in case nobody listens.
>> > > 
>> > > Signed-off-by: Jiri Pirko <jiri@nvidia.com>
>> > > ---
>> > >  net/devlink/dev.c           | 5 ++++-
>> > >  net/devlink/devl_internal.h | 6 ++++++
>> > >  net/devlink/health.c        | 3 +++
>> > >  net/devlink/linecard.c      | 2 +-
>> > >  net/devlink/param.c         | 2 +-
>> > >  net/devlink/port.c          | 2 +-
>> > >  net/devlink/rate.c          | 2 +-
>> > >  net/devlink/region.c        | 2 +-
>> > >  net/devlink/trap.c          | 6 +++---
>> > >  9 files changed, 21 insertions(+), 9 deletions(-)
>> > > 
>> > > diff --git a/net/devlink/dev.c b/net/devlink/dev.c
>> > > index 7c7517e26862..46407689ef70 100644
>> > > --- a/net/devlink/dev.c
>> > > +++ b/net/devlink/dev.c
>> > > @@ -204,6 +204,9 @@ static void devlink_notify(struct devlink *devlink, enum devlink_command cmd)
>> > >  	WARN_ON(cmd != DEVLINK_CMD_NEW && cmd != DEVLINK_CMD_DEL);
>> > >  	WARN_ON(!devl_is_registered(devlink));
>> > 
>> > minor nit: possibly use ASSERT_DEVLINK_REGISTERED(devlink) above?
>> 
>> Sure, but unrelated to this patch.
>> 
>> 
>> > 
>> > >  
>> > > +	if (!devlink_nl_notify_need(devlink))
>> > > +		return;
>> > > +
>> > >  	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
>> > >  	if (!msg)
>> > >  		return;
>> > > @@ -985,7 +988,7 @@ static void __devlink_flash_update_notify(struct devlink *devlink,
>> > >  		cmd != DEVLINK_CMD_FLASH_UPDATE_END &&
>> > >  		cmd != DEVLINK_CMD_FLASH_UPDATE_STATUS);
>> > >  
>> > > -	if (!devl_is_registered(devlink))
>> > > +	if (!devl_is_registered(devlink) || !devlink_nl_notify_need(devlink))
>> > >  		return;
>> > >  
>> > >  	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
>> > > diff --git a/net/devlink/devl_internal.h b/net/devlink/devl_internal.h
>> > > index 59ae4761d10a..510990de094e 100644
>> > > --- a/net/devlink/devl_internal.h
>> > > +++ b/net/devlink/devl_internal.h
>> > > @@ -185,6 +185,12 @@ int devlink_nl_put_nested_handle(struct sk_buff *msg, struct net *net,
>> > >  				 struct devlink *devlink, int attrtype);
>> > >  int devlink_nl_msg_reply_and_new(struct sk_buff **msg, struct genl_info *info);
>> > >  
>> > > +static inline bool devlink_nl_notify_need(struct devlink *devlink)
>> > > +{
>> > > +	return genl_has_listeners(&devlink_nl_family, devlink_net(devlink),
>> > > +				  DEVLINK_MCGRP_CONFIG);
>> > > +}
>> > > +
>> > >  /* Notify */
>> > >  void devlink_notify_register(struct devlink *devlink);
>> > >  void devlink_notify_unregister(struct devlink *devlink);
>> > > diff --git a/net/devlink/health.c b/net/devlink/health.c
>> > > index 71ae121dc739..0795dcf22ca8 100644
>> > > --- a/net/devlink/health.c
>> > > +++ b/net/devlink/health.c
>> > > @@ -496,6 +496,9 @@ static void devlink_recover_notify(struct devlink_health_reporter *reporter,
>> > >  	WARN_ON(cmd != DEVLINK_CMD_HEALTH_REPORTER_RECOVER);
>> > >  	ASSERT_DEVLINK_REGISTERED(devlink);
>> > >  
>> > > +	if (!devlink_nl_notify_need(devlink))
>> > > +		return;
>> > > +
>> > >  	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
>> > >  	if (!msg)
>> > >  		return;
>> > > diff --git a/net/devlink/linecard.c b/net/devlink/linecard.c
>> > > index 9d080ac1734b..45b36975ee6f 100644
>> > > --- a/net/devlink/linecard.c
>> > > +++ b/net/devlink/linecard.c
>> > > @@ -136,7 +136,7 @@ static void devlink_linecard_notify(struct devlink_linecard *linecard,
>> > >  	WARN_ON(cmd != DEVLINK_CMD_LINECARD_NEW &&
>> > >  		cmd != DEVLINK_CMD_LINECARD_DEL);
>> > >  
>> > > -	if (!__devl_is_registered(devlink))
>> > > +	if (!__devl_is_registered(devlink) || !devlink_nl_notify_need(devlink))
>> > >  		return;
>> > >  
>> > >  	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
>> > > diff --git a/net/devlink/param.c b/net/devlink/param.c
>> > > index d74df09311a9..6bb6aee5d937 100644
>> > > --- a/net/devlink/param.c
>> > > +++ b/net/devlink/param.c
>> > > @@ -343,7 +343,7 @@ static void devlink_param_notify(struct devlink *devlink,
>> > >  	 * will replay the notifications if the params are added/removed
>> > >  	 * outside of the lifetime of the instance.
>> > >  	 */
>> > > -	if (!devl_is_registered(devlink))
>> > > +	if (!devlink_nl_notify_need(devlink) || !devl_is_registered(devlink))
>> > 
>> > Minor nit: this is the only statement using this order, perhaps swap
>> > the tests for consistency?
>> 
>> Right. If respin is needed, I'll swap.
>> 
>> 
>> > 
>> > Also possibly add the devlink_nl_notify_need() check in
>> > devl_is_registered to reduce code duplication? plus a
>> 
>> It would be odd to have devlink_nl_notify_need() called from
>> devl_is_registered(). 
>
>Sorry for the confusion, out-of-order on my side. What I really mean
>is: add __devl_is_registered() in devlink_nl_notify_need(). 
>
>> Also, it is non only used on notification paths.
>> I thought about putting the checks in one function, but those are 2
>> separate and unrelated checks, so better to keep them separate.
>
>It looks like devlink_nl_notify_need() implies/requires
>__devl_is_registered() ?
>

__devl_is_registered() and devl_is_registered(), depends on the case.
That's why I prefer to have the check outside devlink_nl_notify_need()


>Cheers,
>
>Paolo
>