netdev - Re: [PATCH net-next v2 18/21] net: ravb: Return cached statistics if the interface is down

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Message-ID: <eed10979-c482-43fe-bbe4-4de5b276e2dd@tuxon.dev>
Date: Sun, 17 Dec 2023 15:54:10 +0200
From: claudiu beznea <claudiu.beznea@...on.dev>
To: Sergey Shtylyov <s.shtylyov@....ru>, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
 richardcochran@...il.com, p.zabel@...gutronix.de,
 yoshihiro.shimoda.uh@...esas.com, wsa+renesas@...g-engineering.com,
 geert+renesas@...der.be
Cc: netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH net-next v2 18/21] net: ravb: Return cached statistics if
 the interface is down



On 16.12.2023 22:02, Sergey Shtylyov wrote:
> On 12/14/23 2:45 PM, Claudiu wrote:
> 
>> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>>
>> Return the cached statistics in case the interface is down. There should be
>> no drawback to this, as most of the statistics are updated on the data path
>> and if runtime PM is enabled and the interface is down, the registers that
>> are explicitly read on ravb_get_stats() are zero anyway on most of the IP
>> variants.
>>
>> The commit prepares the code for the addition of runtime PM support.
>>
>> Suggested-by: Sergey Shtylyov <s.shtylyov@....ru>
>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>> ---
>>
>> Changes in v2:
>> - none; this patch is new
>>
>>  drivers/net/ethernet/renesas/ravb_main.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
>> index a2a64c22ec41..1995cf7ff084 100644
>> --- a/drivers/net/ethernet/renesas/ravb_main.c
>> +++ b/drivers/net/ethernet/renesas/ravb_main.c
>> @@ -2110,6 +2110,9 @@ static struct net_device_stats *ravb_get_stats(struct net_device *ndev)
>>  	const struct ravb_hw_info *info = priv->info;
>>  	struct net_device_stats *nstats, *stats0, *stats1;
>>  
>> +	if (!netif_running(ndev))
> 
>    I'm afraid this is racy as __LINK_STATE_START bit gets set
> by __dev_open() before calling the ndo_open() method... :-(

But (at least on my setup), both ndo_get_stats and ndo_open are called with
rtnl_mutex locked.

> 
>> +		return &ndev->stats;
>> +
> 
>    The sh_eth driver calls sh_eth_get_stats() from sh_eth_dev_exit();
> perhaps it's worth doing something similar?

Indeed, it might help to keep updated those few registers that gets updated
only in ndo_get_stats.


> 
> MBR, Sergey