[PATCH] net: make driver settling time configurable

[PATCH] net: make driver settling time configurable

[David Ventura]

During IP auto configuration, some drivers apparently need to wait a
certain length of time to settle; as this is not true for all drivers,
make this length of time configurable.

Signed-off-by: David Ventura <david@davidv.dev>
---
 .../admin-guide/kernel-parameters.txt         |  4 ++++
 Documentation/admin-guide/nfs/nfsroot.rst     |  3 +++
 net/ipv4/ipconfig.c                           | 23 ++++++++++++++++---
 3 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index b47940577c10..b07a035642fa 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2291,6 +2291,10 @@
 
 	ip=		[IP_PNP]
 			See Documentation/admin-guide/nfs/nfsroot.rst.
+	ip.dev_wait_ms=
+			[IP_PNP]
+			See Documentation/admin-guide/nfs/nfsroot.rst.
+
 
 	ipcmni_extend	[KNL,EARLY] Extend the maximum number of unique System V
 			IPC identifiers from 32,768 to 16,777,216.
diff --git a/Documentation/admin-guide/nfs/nfsroot.rst b/Documentation/admin-guide/nfs/nfsroot.rst
index 135218f33394..f26f7a342af6 100644
--- a/Documentation/admin-guide/nfs/nfsroot.rst
+++ b/Documentation/admin-guide/nfs/nfsroot.rst
@@ -223,6 +223,9 @@ ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:<dns
   /proc/net/ipconfig/ntp_servers to an NTP client before mounting the real
   root filesystem if it is on NFS).
 
+ip.dev_wait_ms=<value>
+  Set the number of milliseconds to delay after opening the network device
+  which will be autoconfigured. Defaults to 10 milliseconds.
 
 nfsrootdebug
   This parameter enables debugging messages to appear in the kernel
diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
index c56b6fe6f0d7..cbf35163b973 100644
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -82,8 +82,6 @@
 #define IPCONFIG_DYNAMIC
 #endif
 
-/* Define the friendly delay before and after opening net devices */
-#define CONF_POST_OPEN		10	/* After opening: 10 msecs */
 
 /* Define the timeout for waiting for a DHCP/BOOTP/RARP reply */
 #define CONF_OPEN_RETRIES 	2	/* (Re)open devices twice */
@@ -101,6 +99,7 @@
 
 /* Wait for carrier timeout default in seconds */
 static unsigned int carrier_timeout = 120;
+static unsigned int dev_wait_ms = 10;
 
 /*
  * Public IP configuration
@@ -1516,7 +1515,8 @@ static int __init ip_auto_config(void)
 		return err;
 
 	/* Give drivers a chance to settle */
-	msleep(CONF_POST_OPEN);
+	if(dev_wait_ms > 0)
+		msleep(dev_wait_ms);
 
 	/*
 	 * If the config information is insufficient (e.g., our IP address or
@@ -1849,3 +1849,20 @@ static int __init set_carrier_timeout(char *str)
 	return 1;
 }
 __setup("carrier_timeout=", set_carrier_timeout);
+
+
+static int __init set_dev_wait_ms(char *str)
+{
+	ssize_t ret;
+
+	if (!str)
+		return 0;
+
+	ret = kstrtouint(str, 0, &dev_wait_ms);
+	if (ret)
+		return 0;
+
+	return 1;
+}
+
+__setup("ip.dev_wait_ms=", set_dev_wait_ms);
-- 
2.39.2

Re: [PATCH] net: make driver settling time configurable

[Andrew Lunn]

On Mon, Feb 05, 2024 at 12:44:40PM +0100, David Ventura wrote:
> During IP auto configuration, some drivers apparently need to wait a
> certain length of time to settle; as this is not true for all drivers,
> make this length of time configurable.

Do you see this problem with multiple drivers, or just one in
particular. To me this seems like a driver bug, and you are just
papering over the cracks.

	Andrew

Re: [PATCH] net: make driver settling time configurable

[David]

On 2/5/24 15:06, Andrew Lunn wrote:
> On Mon, Feb 05, 2024 at 12:44:40PM +0100, David Ventura wrote:
>> During IP auto configuration, some drivers apparently need to wait a
>> certain length of time to settle; as this is not true for all drivers,
>> make this length of time configurable.
> Do you see this problem with multiple drivers, or just one in
> particular. To me this seems like a driver bug, and you are just
> papering over the cracks.
>
> 	Andrew

I haven't seen any problems -- I assumed that some drivers need to wait, 
given

Re: [PATCH] net: make driver settling time configurable

[David]

On 2/5/24 15:06, Andrew Lunn wrote:
> On Mon, Feb 05, 2024 at 12:44:40PM +0100, David Ventura wrote:
>> During IP auto configuration, some drivers apparently need to wait a
>> certain length of time to settle; as this is not true for all drivers,
>> make this length of time configurable.
> Do you see this problem with multiple drivers, or just one in
> particular. To me this seems like a driver bug, and you are just
> papering over the cracks.
>
> 	Andrew
I don't know of any drivers that may need to wait -- I noticed
this code path being hit when building a minimal kernel that only
had a virtio network device.
At least for the virtio device, the wait is unnecessary and bloats
the time to boot a minimal kernel from 15ms to 33ms.

     David

Re: [PATCH] net: make driver settling time configurable

[Andrew Lunn]

On Mon, Feb 05, 2024 at 03:31:38PM +0100, David wrote:
> On 2/5/24 15:06, Andrew Lunn wrote:
> > On Mon, Feb 05, 2024 at 12:44:40PM +0100, David Ventura wrote:
> > > During IP auto configuration, some drivers apparently need to wait a
> > > certain length of time to settle; as this is not true for all drivers,
> > > make this length of time configurable.
> > Do you see this problem with multiple drivers, or just one in
> > particular. To me this seems like a driver bug, and you are just
> > papering over the cracks.
> > 
> > 	Andrew
> I don't know of any drivers that may need to wait -- I noticed
> this code path being hit when building a minimal kernel that only
> had a virtio network device.
> At least for the virtio device, the wait is unnecessary and bloats
> the time to boot a minimal kernel from 15ms to 33ms.

Looking at the code, a delay has been here a long time, since before
git. However, 2011 the delay was changes from 1 second to 10ms. There
was a discussion about this at the time:

https://lore.kernel.org/netdev/1305696161-18277-1-git-send-email-micha@neli.hopto.org/t/

It was said that ARP and DHCP retries should recover any system where
the first transmit/receive gets lost with the change from 1s to 10ms.

Maybe after 12 years, its time to try a default of 0ms? I would
suggest that is a second patch, which is easy to revert if it all goes
horribly wrong.

	 Andrew

[PATCH] net: Change default delay on IP autoconfig to 0ms

[David Ventura]

As suggested, I'm updating the default to 0ms. 

This patch depends on 1f0aa0c947eeb4edb60add141a5bc2309f2dc8dd ("
net: make driver settling time configurable").

Signed-off-by: David Ventura <david@davidv.dev>
---
 Documentation/admin-guide/nfs/nfsroot.rst | 2 +-
 net/ipv4/ipconfig.c                       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/nfs/nfsroot.rst b/Documentation/admin-guide/nfs/nfsroot.rst
index f26f7a342af6..fce610a4ec54 100644
--- a/Documentation/admin-guide/nfs/nfsroot.rst
+++ b/Documentation/admin-guide/nfs/nfsroot.rst
@@ -225,7 +225,7 @@ ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:<dns
 
 ip.dev_wait_ms=<value>
   Set the number of milliseconds to delay after opening the network device
-  which will be autoconfigured. Defaults to 10 milliseconds.
+  which will be autoconfigured. Defaults to 0 milliseconds.
 
 nfsrootdebug
   This parameter enables debugging messages to appear in the kernel
diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
index cbf35163b973..8b7d08649b09 100644
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -99,7 +99,7 @@
 
 /* Wait for carrier timeout default in seconds */
 static unsigned int carrier_timeout = 120;
-static unsigned int dev_wait_ms = 10;
+static unsigned int dev_wait_ms = 0;
 
 /*
  * Public IP configuration
-- 
2.39.2

Re: [PATCH] net: Change default delay on IP autoconfig to 0ms

[Jakub Kicinski]

On Mon,  5 Feb 2024 16:55:43 +0100 David Ventura wrote:
> As suggested, I'm updating the default to 0ms. 
> 
> This patch depends on 1f0aa0c947eeb4edb60add141a5bc2309f2dc8dd ("
> net: make driver settling time configurable").

Please post a v2, in a new thread, and proper commit description
with a link to the discussion with Andrew.