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

Jiri Pirko
2023-11-27T12:04:22Z

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(). 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.

>__devl_is_registered() variant for the 2 cases above not requiring the
>additional check.
>
>No need to repost for the above.
>
>Cheers,
>
>Paolo
>