[PATCH v1 net] lan743x: fix return value for lan743x_tx_napi_poll

[PATCH v1 net] lan743x: fix return value for lan743x_tx_napi_poll

[Bryan Whitehead]

It has been noticed that under stress the lan743x driver will
sometimes hang or cause a kernel panic. It has been noticed
that returning '0' instead of 'weight' fixes this issue.

fixes: rare kernel panic under heavy traffic load.
Signed-off-by: Bryan Whitehead <Bryan.Whitehead@microchip.com>
---
 drivers/net/ethernet/microchip/lan743x_main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/microchip/lan743x_main.c b/drivers/net/ethernet/microchip/lan743x_main.c
index 867cddb..ca33ade 100644
--- a/drivers/net/ethernet/microchip/lan743x_main.c
+++ b/drivers/net/ethernet/microchip/lan743x_main.c
@@ -1672,7 +1672,7 @@ static int lan743x_tx_napi_poll(struct napi_struct *napi, int weight)
 		netif_wake_queue(adapter->netdev);
 	}
 
-	if (!napi_complete_done(napi, weight))
+	if (!napi_complete_done(napi, 0))
 		goto done;
 
 	/* enable isr */
@@ -1681,7 +1681,7 @@ static int lan743x_tx_napi_poll(struct napi_struct *napi, int weight)
 	lan743x_csr_read(adapter, INT_STS);
 
 done:
-	return weight;
+	return 0;
 }
 
 static void lan743x_tx_ring_cleanup(struct lan743x_tx *tx)
-- 
2.7.4

Re: [PATCH v1 net] lan743x: fix return value for lan743x_tx_napi_poll

[Andrew Lunn]

On Tue, Nov 20, 2018 at 01:26:43PM -0500, Bryan Whitehead wrote:
> It has been noticed that under stress the lan743x driver will
> sometimes hang or cause a kernel panic. It has been noticed
> that returning '0' instead of 'weight' fixes this issue.
> 
> fixes: rare kernel panic under heavy traffic load.
> Signed-off-by: Bryan Whitehead <Bryan.Whitehead@microchip.com>

Hi Bryan

This sounds like a band aid over something which is broken, not a real
fix.

Can you show us the stack trace from the panic?

    Andrew

RE: [PATCH v1 net] lan743x: fix return value for lan743x_tx_napi_poll

[Bryan.Whitehead]

> -----Original Message-----
> From: Andrew Lunn <andrew@lunn.ch>
> Sent: Tuesday, November 20, 2018 2:31 PM
> To: Bryan Whitehead - C21958 <Bryan.Whitehead@microchip.com>
> Cc: davem@davemloft.net; netdev@vger.kernel.org; UNGLinuxDriver
> <UNGLinuxDriver@microchip.com>
> Subject: Re: [PATCH v1 net] lan743x: fix return value for
> lan743x_tx_napi_poll
> 
> On Tue, Nov 20, 2018 at 01:26:43PM -0500, Bryan Whitehead wrote:
> > It has been noticed that under stress the lan743x driver will
> > sometimes hang or cause a kernel panic. It has been noticed that
> > returning '0' instead of 'weight' fixes this issue.
> >
> > fixes: rare kernel panic under heavy traffic load.
> > Signed-off-by: Bryan Whitehead <Bryan.Whitehead@microchip.com>
> 
> Hi Bryan
> 
> This sounds like a band aid over something which is broken, not a real fix.
> 
> Can you show us the stack trace from the panic?
> 
>     Andrew

Andrew,

Admittedly, my knowledge of what the kernel is doing behind the scenes is limited.

But according to documentation found on 
https://wiki.linuxfoundation.org/networking/napi

It states the following
"The poll() function may also process TX completions, in which case if it processes
the entire TX ring then it should count that work as the rest of the budget.
Otherwise, TX completions are not counted."

So based on that, the original driver was returning the full budget. But I was having
Issues with it. And the above documentation seems to suggest that I could return 0
As in "not counted" from above.

I tried it, and my lock up issues disappeared.

Regarding the kernel panic stack trace. So far its very hard to replicate that on the 
latest kernel. I've seen it more frequently when back porting to older kernels such
as 4.14, and 4.9. This same fix caused those kernel panics to disappear.
Are you interested in seeing a stack dump from older kernels?

In the latest kernel the issue manifests as a kernel message which states
"[  945.021101] enp48s0: Budget exhausted after napi rescheduled"

I'm not sure what that means. But it does not lock up immediately after seeing that
Message. But it usually locks up with in a minute of seeing that message.

And the sometimes I get the following warning
[ 1240.425020] ------------[ cut here ]------------
[ 1240.426014] NETDEV WATCHDOG: enp0s25 (e1000e): transmit queue 0 timed out
[ 1240.430027] WARNING: CPU: 0 PID: 0 at net/sched/sch_generic.c:461 dev_watchdog+0x1ef/0x200
[ 1240.430027] Modules linked in: lan743x
[ 1240.430027] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G          I       4.19.2 #1
[ 1240.430027] Hardware name: Hewlett-Packard HP Compaq dc7900 Convertible Minitower/3032h, BIOS 786G1 v01.16 03/05/2009
[ 1240.430027] RIP: 0010:dev_watchdog+0x1ef/0x200
[ 1240.430027] Code: 00 48 63 4d e0 eb 93 4c 89 e7 c6 05 68 30 b3 00 01 e8 25 3d fd ff 89 d9 48 89 c2 4c 89 e6 48 c7 c7 98 92 48 ab e8 f1 28 87 ff <0f> 0b eb c0 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 48 c7 47 08 00
[ 1240.430027] RSP: 0018:ffff98490be03e90 EFLAGS: 00010282
[ 1240.430027] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
[ 1240.497168] RDX: 0000000000040400 RSI: 00000000000000f6 RDI: 0000000000000300
[ 1240.497168] RBP: ffff984908574440 R08: 0000000000000000 R09: 00000000000003a4
[ 1240.497168] R10: 0000000000000020 R11: ffffffffabc928ed R12: ffff984908574000
[ 1240.497168] R13: 0000000000000000 R14: 0000000000000000 R15: ffff98490be195b0
[ 1240.497168] FS:  0000000000000000(0000) GS:ffff98490be00000(0000) knlGS:0000000000000000
[ 1240.497168] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1240.497168] CR2: 00007f31cd4c0000 CR3: 0000000109bca000 CR4: 00000000000406f0
[ 1240.497168] Call Trace:
[ 1240.497168]  <IRQ>
[ 1240.497168]  ? qdisc_reset+0xe0/0xe0
[ 1240.497168]  call_timer_fn+0x26/0x130
[ 1240.497168]  run_timer_softirq+0x1cd/0x400
[ 1240.497168]  ? hpet_interrupt_handler+0x10/0x30
[ 1240.497168]  __do_softirq+0xed/0x2aa
[ 1240.497168]  irq_exit+0xb7/0xc0
[ 1240.497168]  do_IRQ+0x45/0xd0
[ 1240.497168]  common_interrupt+0xf/0xf
[ 1240.497168]  </IRQ>
[ 1240.497168] RIP: 0010:cpuidle_enter_state+0xa6/0x330
[ 1240.497168] Code: 65 8b 3d 1d b0 4d 55 e8 58 6a 95 ff 48 89 c3 66 66 66 66 90 31 ff e8 59 73 95 ff 80 7c 24 0b 00 0f 85 25 02 00 00 fb 4c 29 eb <48> ba cf f7 53 e3 a5 9b c4 20 48 89 d8 48 c1 fb 3f 48 f7 ea b8 ff
[ 1240.497168] RSP: 0018:ffffffffab603e60 EFLAGS: 00000216 ORIG_RAX: ffffffffffffffde
[ 1240.497168] RAX: ffff98490be20a80 RBX: 000000000081035c RCX: 00000120cf178c49
[ 1240.497168] RDX: 00000120cf178ca0 RSI: 00000120cf178ca0 RDI: 0000000000000000
[ 1240.497168] RBP: ffff984908fbd000 R08: fffffffb58ea5f9e R09: 000001208e0b48df
[ 1240.497168] R10: 00000000000018c4 R11: 0000000000002468 R12: 0000000000000002
[ 1240.497168] R13: 00000120ce968944 R14: ffffffffab6a68a0 R15: ffffffffab611740
[ 1240.497168]  do_idle+0x1da/0x230
[ 1240.497168]  cpu_startup_entry+0x6a/0x70
[ 1240.497168]  start_kernel+0x4a2/0x4c2
[ 1240.497168]  secondary_startup_64+0xa4/0xb0
[ 1240.497168] ---[ end trace c6f3be34c214db4e ]---

Notice the warning is referring to a different adapter. So I suspect that whatever happened it froze
All network adapters.

If you have suggestions let me know.

Or if you would like to see the kernel panics from older kernels let me know.

Regards,
Bryan

Re: [PATCH v1 net] lan743x: fix return value for lan743x_tx_napi_poll

[Andrew Lunn]

> Andrew,
> 
> Admittedly, my knowledge of what the kernel is doing behind the
> scenes is limited.

Me too. Lets see if anybody can make sense of the information you
provided.

Thanks
   Andrew

Re: [PATCH v1 net] lan743x: fix return value for lan743x_tx_napi_poll

[Florian Fainelli]

On 11/20/18 1:39 PM, Bryan.Whitehead@microchip.com wrote:
>> -----Original Message-----
>> From: Andrew Lunn <andrew@lunn.ch>
>> Sent: Tuesday, November 20, 2018 2:31 PM
>> To: Bryan Whitehead - C21958 <Bryan.Whitehead@microchip.com>
>> Cc: davem@davemloft.net; netdev@vger.kernel.org; UNGLinuxDriver
>> <UNGLinuxDriver@microchip.com>
>> Subject: Re: [PATCH v1 net] lan743x: fix return value for
>> lan743x_tx_napi_poll
>>
>> On Tue, Nov 20, 2018 at 01:26:43PM -0500, Bryan Whitehead wrote:
>>> It has been noticed that under stress the lan743x driver will
>>> sometimes hang or cause a kernel panic. It has been noticed that
>>> returning '0' instead of 'weight' fixes this issue.
>>>
>>> fixes: rare kernel panic under heavy traffic load.
>>> Signed-off-by: Bryan Whitehead <Bryan.Whitehead@microchip.com>
>>
>> Hi Bryan
>>
>> This sounds like a band aid over something which is broken, not a real fix.
>>
>> Can you show us the stack trace from the panic?
>>
>>     Andrew
> 
> Andrew,
> 
> Admittedly, my knowledge of what the kernel is doing behind the scenes is limited.
> 
> But according to documentation found on 
> https://wiki.linuxfoundation.org/networking/napi
> 
> It states the following
> "The poll() function may also process TX completions, in which case if it processes
> the entire TX ring then it should count that work as the rest of the budget.
> Otherwise, TX completions are not counted."
> 
> So based on that, the original driver was returning the full budget. But I was having
> Issues with it. And the above documentation seems to suggest that I could return 0
> As in "not counted" from above.
> 
> I tried it, and my lock up issues disappeared.
> 
> Regarding the kernel panic stack trace. So far its very hard to replicate that on the 
> latest kernel. I've seen it more frequently when back porting to older kernels such
> as 4.14, and 4.9. This same fix caused those kernel panics to disappear.
> Are you interested in seeing a stack dump from older kernels?
> 
> In the latest kernel the issue manifests as a kernel message which states
> "[  945.021101] enp48s0: Budget exhausted after napi rescheduled"
> 
> I'm not sure what that means. But it does not lock up immediately after seeing that
> Message. But it usually locks up with in a minute of seeing that message.
> 
> And the sometimes I get the following warning
> [ 1240.425020] ------------[ cut here ]------------
> [ 1240.426014] NETDEV WATCHDOG: enp0s25 (e1000e): transmit queue 0 timed out
> [ 1240.430027] WARNING: CPU: 0 PID: 0 at net/sched/sch_generic.c:461 dev_watchdog+0x1ef/0x200
> [ 1240.430027] Modules linked in: lan743x
> [ 1240.430027] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G          I       4.19.2 #1
> [ 1240.430027] Hardware name: Hewlett-Packard HP Compaq dc7900 Convertible Minitower/3032h, BIOS 786G1 v01.16 03/05/2009
> [ 1240.430027] RIP: 0010:dev_watchdog+0x1ef/0x200
> [ 1240.430027] Code: 00 48 63 4d e0 eb 93 4c 89 e7 c6 05 68 30 b3 00 01 e8 25 3d fd ff 89 d9 48 89 c2 4c 89 e6 48 c7 c7 98 92 48 ab e8 f1 28 87 ff <0f> 0b eb c0 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 48 c7 47 08 00
> [ 1240.430027] RSP: 0018:ffff98490be03e90 EFLAGS: 00010282
> [ 1240.430027] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> [ 1240.497168] RDX: 0000000000040400 RSI: 00000000000000f6 RDI: 0000000000000300
> [ 1240.497168] RBP: ffff984908574440 R08: 0000000000000000 R09: 00000000000003a4
> [ 1240.497168] R10: 0000000000000020 R11: ffffffffabc928ed R12: ffff984908574000
> [ 1240.497168] R13: 0000000000000000 R14: 0000000000000000 R15: ffff98490be195b0
> [ 1240.497168] FS:  0000000000000000(0000) GS:ffff98490be00000(0000) knlGS:0000000000000000
> [ 1240.497168] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 1240.497168] CR2: 00007f31cd4c0000 CR3: 0000000109bca000 CR4: 00000000000406f0
> [ 1240.497168] Call Trace:
> [ 1240.497168]  <IRQ>
> [ 1240.497168]  ? qdisc_reset+0xe0/0xe0
> [ 1240.497168]  call_timer_fn+0x26/0x130
> [ 1240.497168]  run_timer_softirq+0x1cd/0x400
> [ 1240.497168]  ? hpet_interrupt_handler+0x10/0x30
> [ 1240.497168]  __do_softirq+0xed/0x2aa
> [ 1240.497168]  irq_exit+0xb7/0xc0
> [ 1240.497168]  do_IRQ+0x45/0xd0
> [ 1240.497168]  common_interrupt+0xf/0xf
> [ 1240.497168]  </IRQ>
> [ 1240.497168] RIP: 0010:cpuidle_enter_state+0xa6/0x330
> [ 1240.497168] Code: 65 8b 3d 1d b0 4d 55 e8 58 6a 95 ff 48 89 c3 66 66 66 66 90 31 ff e8 59 73 95 ff 80 7c 24 0b 00 0f 85 25 02 00 00 fb 4c 29 eb <48> ba cf f7 53 e3 a5 9b c4 20 48 89 d8 48 c1 fb 3f 48 f7 ea b8 ff
> [ 1240.497168] RSP: 0018:ffffffffab603e60 EFLAGS: 00000216 ORIG_RAX: ffffffffffffffde
> [ 1240.497168] RAX: ffff98490be20a80 RBX: 000000000081035c RCX: 00000120cf178c49
> [ 1240.497168] RDX: 00000120cf178ca0 RSI: 00000120cf178ca0 RDI: 0000000000000000
> [ 1240.497168] RBP: ffff984908fbd000 R08: fffffffb58ea5f9e R09: 000001208e0b48df
> [ 1240.497168] R10: 00000000000018c4 R11: 0000000000002468 R12: 0000000000000002
> [ 1240.497168] R13: 00000120ce968944 R14: ffffffffab6a68a0 R15: ffffffffab611740
> [ 1240.497168]  do_idle+0x1da/0x230
> [ 1240.497168]  cpu_startup_entry+0x6a/0x70
> [ 1240.497168]  start_kernel+0x4a2/0x4c2
> [ 1240.497168]  secondary_startup_64+0xa4/0xb0
> [ 1240.497168] ---[ end trace c6f3be34c214db4e ]---
> 
> Notice the warning is referring to a different adapter. So I suspect that whatever happened it froze
> All network adapters.
> 
> If you have suggestions let me know.

Did you look at the output of "perf top" or something along those lines
to figure out if your lan743x driver is indeed responsible for that by
not being scheduler friendly? What is likely happening is that you do
not reclaim "weight" packets and instead keep looping into NAPI context,
which prevents the system from making further progress.

Calling napi_complete_done() for the TX path is not necessary AFAICT,
what you really want to do is call napi_complete() and make sure you:

- reclaim/free as many TX buffers as possible, without looking at the
NAPI weight which becomes irrelevant
- if you have been able to reclaim enough descriptors, wake-up the
transmit queue

So ignoring the NAPI weight like you do is correct, but calling
napi_complete_done() with a 0 argument does not sound correct to me.
-- 
Florian

RE: [PATCH v1 net] lan743x: fix return value for lan743x_tx_napi_poll

[Tristram.Ha]

Slightly out of topic I am not sure why NAPI is used on the transmit side.
Originally NAPI was designed to fix the receive interrupt happening on each
receive frame problem, so on transmit side it is to avoid the transmit
done interrupt on each transmit frame?  Typically hardware has a way
to trigger transmit done interrupt or not in each transmit frame.

NAPI may have other uses in newer kernels that I am not aware of.

I notice 2 problems in the driver:

1. netif_napi_add is used instead of netif_tx_napi_add.
2. In all other drivers that use netif_tx_napi_add most do not call napi_complete_done.
They all call napi_complete directly and return 0.

freescale/gianfar.c
rocker/rocker_main.c
ti/cpsw.c

virtio_net.c does use napi_complete_done but it also passes 0 as a parameter.


> -----Original Message-----
> From: Florian Fainelli <f.fainelli@gmail.com>
> Sent: Tuesday, November 20, 2018 2:12 PM
> To: Bryan Whitehead - C21958 <Bryan.Whitehead@microchip.com>;
> andrew@lunn.ch
> Cc: davem@davemloft.net; netdev@vger.kernel.org; UNGLinuxDriver
> <UNGLinuxDriver@microchip.com>
> Subject: Re: [PATCH v1 net] lan743x: fix return value for
> lan743x_tx_napi_poll
> 
> On 11/20/18 1:39 PM, Bryan.Whitehead@microchip.com wrote:
> >> -----Original Message-----
> >> From: Andrew Lunn <andrew@lunn.ch>
> >> Sent: Tuesday, November 20, 2018 2:31 PM
> >> To: Bryan Whitehead - C21958 <Bryan.Whitehead@microchip.com>
> >> Cc: davem@davemloft.net; netdev@vger.kernel.org; UNGLinuxDriver
> >> <UNGLinuxDriver@microchip.com>
> >> Subject: Re: [PATCH v1 net] lan743x: fix return value for
> >> lan743x_tx_napi_poll
> >>
> >> On Tue, Nov 20, 2018 at 01:26:43PM -0500, Bryan Whitehead wrote:
> >>> It has been noticed that under stress the lan743x driver will
> >>> sometimes hang or cause a kernel panic. It has been noticed that
> >>> returning '0' instead of 'weight' fixes this issue.
> >>>
> >>> fixes: rare kernel panic under heavy traffic load.
> >>> Signed-off-by: Bryan Whitehead <Bryan.Whitehead@microchip.com>
> >>
> >> Hi Bryan
> >>
> >> This sounds like a band aid over something which is broken, not a real fix.
> >>
> >> Can you show us the stack trace from the panic?
> >>
> >>     Andrew
> >
> > Andrew,
> >
> > Admittedly, my knowledge of what the kernel is doing behind the scenes is
> limited.
> >
> > But according to documentation found on
> > https://wiki.linuxfoundation.org/networking/napi
> >
> > It states the following
> > "The poll() function may also process TX completions, in which case if it
> processes
> > the entire TX ring then it should count that work as the rest of the budget.
> > Otherwise, TX completions are not counted."
> >
> > So based on that, the original driver was returning the full budget. But I was
> having
> > Issues with it. And the above documentation seems to suggest that I could
> return 0
> > As in "not counted" from above.
> >
> > I tried it, and my lock up issues disappeared.
> >
> > Regarding the kernel panic stack trace. So far its very hard to replicate that
> on the
> > latest kernel. I've seen it more frequently when back porting to older
> kernels such
> > as 4.14, and 4.9. This same fix caused those kernel panics to disappear.
> > Are you interested in seeing a stack dump from older kernels?
> >
> > In the latest kernel the issue manifests as a kernel message which states
> > "[  945.021101] enp48s0: Budget exhausted after napi rescheduled"
> >
> > I'm not sure what that means. But it does not lock up immediately after
> seeing that
> > Message. But it usually locks up with in a minute of seeing that message.
> >
> > And the sometimes I get the following warning
> > [ 1240.425020] ------------[ cut here ]------------
> > [ 1240.426014] NETDEV WATCHDOG: enp0s25 (e1000e): transmit queue 0
> timed out
> > [ 1240.430027] WARNING: CPU: 0 PID: 0 at net/sched/sch_generic.c:461
> dev_watchdog+0x1ef/0x200
> > [ 1240.430027] Modules linked in: lan743x
> > [ 1240.430027] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G          I       4.19.2 #1
> > [ 1240.430027] Hardware name: Hewlett-Packard HP Compaq dc7900
> Convertible Minitower/3032h, BIOS 786G1 v01.16 03/05/2009
> > [ 1240.430027] RIP: 0010:dev_watchdog+0x1ef/0x200
> > [ 1240.430027] Code: 00 48 63 4d e0 eb 93 4c 89 e7 c6 05 68 30 b3 00 01 e8 25
> 3d fd ff 89 d9 48 89 c2 4c 89 e6 48 c7 c7 98 92 48 ab e8 f1 28 87 ff <0f> 0b eb c0
> 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 48 c7 47 08 00
> > [ 1240.430027] RSP: 0018:ffff98490be03e90 EFLAGS: 00010282
> > [ 1240.430027] RAX: 0000000000000000 RBX: 0000000000000000 RCX:
> 0000000000000000
> > [ 1240.497168] RDX: 0000000000040400 RSI: 00000000000000f6 RDI:
> 0000000000000300
> > [ 1240.497168] RBP: ffff984908574440 R08: 0000000000000000 R09:
> 00000000000003a4
> > [ 1240.497168] R10: 0000000000000020 R11: ffffffffabc928ed R12:
> ffff984908574000
> > [ 1240.497168] R13: 0000000000000000 R14: 0000000000000000 R15:
> ffff98490be195b0
> > [ 1240.497168] FS:  0000000000000000(0000) GS:ffff98490be00000(0000)
> knlGS:0000000000000000
> > [ 1240.497168] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [ 1240.497168] CR2: 00007f31cd4c0000 CR3: 0000000109bca000 CR4:
> 00000000000406f0
> > [ 1240.497168] Call Trace:
> > [ 1240.497168]  <IRQ>
> > [ 1240.497168]  ? qdisc_reset+0xe0/0xe0
> > [ 1240.497168]  call_timer_fn+0x26/0x130
> > [ 1240.497168]  run_timer_softirq+0x1cd/0x400
> > [ 1240.497168]  ? hpet_interrupt_handler+0x10/0x30
> > [ 1240.497168]  __do_softirq+0xed/0x2aa
> > [ 1240.497168]  irq_exit+0xb7/0xc0
> > [ 1240.497168]  do_IRQ+0x45/0xd0
> > [ 1240.497168]  common_interrupt+0xf/0xf
> > [ 1240.497168]  </IRQ>
> > [ 1240.497168] RIP: 0010:cpuidle_enter_state+0xa6/0x330
> > [ 1240.497168] Code: 65 8b 3d 1d b0 4d 55 e8 58 6a 95 ff 48 89 c3 66 66 66 66
> 90 31 ff e8 59 73 95 ff 80 7c 24 0b 00 0f 85 25 02 00 00 fb 4c 29 eb <48> ba cf f7
> 53 e3 a5 9b c4 20 48 89 d8 48 c1 fb 3f 48 f7 ea b8 ff
> > [ 1240.497168] RSP: 0018:ffffffffab603e60 EFLAGS: 00000216 ORIG_RAX:
> ffffffffffffffde
> > [ 1240.497168] RAX: ffff98490be20a80 RBX: 000000000081035c RCX:
> 00000120cf178c49
> > [ 1240.497168] RDX: 00000120cf178ca0 RSI: 00000120cf178ca0 RDI:
> 0000000000000000
> > [ 1240.497168] RBP: ffff984908fbd000 R08: fffffffb58ea5f9e R09:
> 000001208e0b48df
> > [ 1240.497168] R10: 00000000000018c4 R11: 0000000000002468 R12:
> 0000000000000002
> > [ 1240.497168] R13: 00000120ce968944 R14: ffffffffab6a68a0 R15:
> ffffffffab611740
> > [ 1240.497168]  do_idle+0x1da/0x230
> > [ 1240.497168]  cpu_startup_entry+0x6a/0x70
> > [ 1240.497168]  start_kernel+0x4a2/0x4c2
> > [ 1240.497168]  secondary_startup_64+0xa4/0xb0
> > [ 1240.497168] ---[ end trace c6f3be34c214db4e ]---
> >
> > Notice the warning is referring to a different adapter. So I suspect that
> whatever happened it froze
> > All network adapters.
> >
> > If you have suggestions let me know.
> 
> Did you look at the output of "perf top" or something along those lines
> to figure out if your lan743x driver is indeed responsible for that by
> not being scheduler friendly? What is likely happening is that you do
> not reclaim "weight" packets and instead keep looping into NAPI context,
> which prevents the system from making further progress.
> 
> Calling napi_complete_done() for the TX path is not necessary AFAICT,
> what you really want to do is call napi_complete() and make sure you:
> 
> - reclaim/free as many TX buffers as possible, without looking at the
> NAPI weight which becomes irrelevant
> - if you have been able to reclaim enough descriptors, wake-up the
> transmit queue
> 
> So ignoring the NAPI weight like you do is correct, but calling
> napi_complete_done() with a 0 argument does not sound correct to me.
> --
> Florian

Re: [PATCH v1 net] lan743x: fix return value for lan743x_tx_napi_poll

[David Miller]

From: <Tristram.Ha@microchip.com>
Date: Wed, 21 Nov 2018 02:13:30 +0000

> Slightly out of topic I am not sure why NAPI is used on the transmit side.
> Originally NAPI was designed to fix the receive interrupt happening on each
> receive frame problem, so on transmit side it is to avoid the transmit
> done interrupt on each transmit frame?  Typically hardware has a way
> to trigger transmit done interrupt or not in each transmit frame.

It puts transmit completion, like receive processing, inside of a
software instead of a hardware interrupt.

It is very much intended that all drivers do transmit completion
inside of a NAPI context.

Avoiding TX interrupts by clearing interrupt indication bits in the
TX descriptors or turning TX completion interrupts off compeltely
is a non-starter.

All TX completion events MUST occur in a short finite amount of time,
otherwise you wedge TCP sockets waiting for memory to be free'd up
etc.

RE: [PATCH v1 net] lan743x: fix return value for lan743x_tx_napi_poll

[Bryan.Whitehead]

> Did you look at the output of "perf top" or something along those lines to
> figure out if your lan743x driver is indeed responsible for that by not being
> scheduler friendly? What is likely happening is that you do not reclaim
> "weight" packets and instead keep looping into NAPI context, which
> prevents the system from making further progress.
> 
I'm having trouble installing "perf" for my kernel. But I have used GPIO's and a scope
To make sure my poll routine is called and returns in a timely manner. I've never seen
A problem with it "not being scheduler friendly"

> Calling napi_complete_done() for the TX path is not necessary AFAICT, what
> you really want to do is call napi_complete() and make sure you:
> 
> - reclaim/free as many TX buffers as possible, without looking at the NAPI
> weight which becomes irrelevant
> - if you have been able to reclaim enough descriptors, wake-up the transmit
> queue
> 
> So ignoring the NAPI weight like you do is correct, but calling
> napi_complete_done() with a 0 argument does not sound correct to me.
> --
> Florian

I see that napi_complete just maps to napi_complete_done with a 0 argument anyway.
So they are currently functionally identical, but I will make a new version that uses
napi_complete as you suggested.

But it seems you would definitely agree that the previous version of lan743x driver
Which called napi_complete_done with 'weight' as the argument is wrong,
And therefor this fix is correct.

RE: [PATCH v1 net] lan743x: fix return value for lan743x_tx_napi_poll

[Bryan.Whitehead]

> I notice 2 problems in the driver:
> 
> 1. netif_napi_add is used instead of netif_tx_napi_add.
> 2. In all other drivers that use netif_tx_napi_add most do not call
> napi_complete_done.
> They all call napi_complete directly and return 0.
> 
> freescale/gianfar.c
> rocker/rocker_main.c
> ti/cpsw.c
> 
> virtio_net.c does use napi_complete_done but it also passes 0 as a
> parameter.
> 
Tristram,

Thanks for the tips. I will make a new version which uses
  netif_tx_napi_add, and napi_complete

Regards,
Bryan