netdev - Re: [BUG] 3.19-rc1 net: less interrupt masking in NAPI

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Date:	Sat, 10 Jan 2015 13:10:25 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Oded Gabbay <oded.gabbay@....com>,
	Johannes Berg <johannes.berg@...el.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Willem de Bruijn <willemb@...gle.com>,
	"Bridgman, John" <John.Bridgman@....com>,
	"Elifaz, Dana" <Dana.Elifaz@....com>
Subject: Re: [BUG] 3.19-rc1 net: less interrupt masking in NAPI

On Sat, 2015-01-10 at 12:58 -0800, Eric Dumazet wrote:
> On Sat, 2015-01-10 at 22:39 +0200, Oded Gabbay wrote:
> > Hi,
> > 
> > Commit d75b1ade567ffab085e8adbbdacf0092d10cd09c breaks my "Qualcomm Atheros
> > AR8161 Gigabit Ethernet (rev 10)" Ethernet controller, which is handled by
> > the alx network driver.
> > 
> > ogabbay@...dg-ubuntu:~$ lspci -s 01:00.0 -k
> > 01:00.0 Ethernet controller:
> > 	Qualcomm Atheros AR8161 Gigabit Ethernet (rev 10)
> > 	Subsystem: Qualcomm Atheros Device 1071
> > 	Kernel driver in use: alx
> > 
> > I have this controller on a mobile platform of AMD APU Kaveri, which I use
> > to test amdkfd, and from 3.19-rc1 the network stopped working when trying to
> > transfer files through scp or nfs.
> > 
> > I bisected the kernel (from 3.18.0 to 3.19-rc1) and reached this commit.
> > 
> > Here is the log of the bisect:
> > 
> > git bisect start
> > # bad: [97bf6af1f928216fd6c5a66e8a57bfa95a659672] Linux 3.19-rc1
> > git bisect bad 97bf6af1f928216fd6c5a66e8a57bfa95a659672
> > 
> > # good: [b2776bf7149bddd1f4161f14f79520f17fc1d71d] Linux 3.18
> > git bisect good b2776bf7149bddd1f4161f14f79520f17fc1d71d
> > 
> > # bad: [70e71ca0af244f48a5dcf56dc435243792e3a495] Merge
> > git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next
> > git bisect bad 70e71ca0af244f48a5dcf56dc435243792e3a495
> > 
> > # good: [e28870f9b3e92cd3570925089c6bb789c2603bc4] Merge tag
> > 'backlight-for-linus-3.19' of
> > git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight
> > git bisect good e28870f9b3e92cd3570925089c6bb789c2603bc4
> > 
> > # bad: [450fa21942fe2c37f0c9f52d1a33bbc081eee288] sh_eth: Remove redundant
> > alignment adjustment
> > git bisect bad 450fa21942fe2c37f0c9f52d1a33bbc081eee288
> > 
> > # bad: [5c8d19da950861d0482abc0ac3481acca34b008f] e100e: use
> > netdev_rss_key_fill() helper
> > git bisect bad 5c8d19da950861d0482abc0ac3481acca34b008f
> > 
> > # good: [bf515fb11ab539c76d04f0e3c5216ed41f41d81f] Merge tag
> > 'mac80211-next-for-john-2014-11-04' of
> > git://git.kernel.org/pub/scm/linux/kernel/git/jberg/mac80211-next
> > git bisect good bf515fb11ab539c76d04f0e3c5216ed41f41d81f
> > 
> > # bad: [2c99cd914d4fed9160d98849c9dd38034616768e] Merge branch 'amd-xgbe-next'
> > git bisect bad 2c99cd914d4fed9160d98849c9dd38034616768e
> > 
> > # good: [3d762a0f0ab9cb4a6b5993db3ce56c92f9f90ab2] net: dsa: Add support for
> > reading switch registers with ethtool
> > git bisect good 3d762a0f0ab9cb4a6b5993db3ce56c92f9f90ab2
> > 
> > # bad: [8ce0c8254f15229aa99fc6c04141f28c446e5f8c] Merge branch 'master' of
> > git://git.kernel.org/pub/scm/linux/kernel/git/jkirsher/net-next
> > git bisect bad 8ce0c8254f15229aa99fc6c04141f28c446e5f8c
> > 
> > # good: [f0c65567b3c1b23f79e8a49139580a3872a68d1f] Merge branch
> > 'sunvnet-multi-tx-queue'
> > git bisect good f0c65567b3c1b23f79e8a49139580a3872a68d1f
> > 
> > # bad: [547f2735c20023d7b50a791b1b17cacb652e9237] Merge branch 'mlx4-next'
> > git bisect bad 547f2735c20023d7b50a791b1b17cacb652e9237
> > 
> > # good: [4cdb1e2e3d3495423db558d3bb7ed11d66aabce7] net: shrink struct
> > softnet_data
> > git bisect good 4cdb1e2e3d3495423db558d3bb7ed11d66aabce7
> > 
> > # bad: [0a98455666ec87378148a1dde97f1ce5baf75a64] net/mlx4_core: Protect
> > port type setting by mutex
> > git bisect bad 0a98455666ec87378148a1dde97f1ce5baf75a64
> > 
> > # bad: [6e8066999800d90d52af5c84ac49ebf683d14cdc] net/mlx4_core: Prevent VF
> > from changing port configuration
> > git bisect bad 6e8066999800d90d52af5c84ac49ebf683d14cdc
> > 
> > # bad: [d75b1ade567ffab085e8adbbdacf0092d10cd09c] net: less interrupt
> > masking in NAPI
> > git bisect bad d75b1ade567ffab085e8adbbdacf0092d10cd09c
> > 
> > # first bad commit: [d75b1ade567ffab085e8adbbdacf0092d10cd09c]
> > net: less interrupt masking in NAPI
> > 
> > Could you please solve this issue as it renders my board quite useless.
> > 
> 
> Thanks for the report and bisection !
> 
> Could you try following fix ?
> 
> diff --git a/drivers/net/ethernet/atheros/alx/main.c b/drivers/net/ethernet/atheros/alx/main.c
> index e398eda07298..209c40765e0d 100644
> --- a/drivers/net/ethernet/atheros/alx/main.c
> +++ b/drivers/net/ethernet/atheros/alx/main.c
> @@ -272,7 +272,7 @@ static int alx_poll(struct napi_struct *napi, int budget)
>  		   alx_clean_rx_irq(alx, budget);
>  
>  	if (!complete)
> -		return 1;
> +		return budget;
>  
>  	napi_complete(&alx->napi);
>  
> 
> 
> 

BTW this driver has other issues :

complete = alx_clean_tx_irq(alx) &&
            alx_clean_rx_irq(alx, budget);

Means that under TX completion pressure (alx_clean_tx_irq(alx) return
false), we never dequeue packets from RX rings.



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