Re: [PATCH 3.3.0-rc1 1/2] do_mounts: Change the nfs-mount retry min max delays.

[Srinivas KANDAGATLA <srinivas.kandagatla@st.com>]

Chuck Lever wrote:
> On Jan 26, 2012, at 9:42 AM, Srinivas KANDAGATLA wrote:
>
>   
>> From: Srinivas Kandagatla <srinivas.kandagatla@st.com>
>>
>> This patch attempts to minimize the delay in nfs root mount, which
>> happens as side effect of nfs-root mount retry by changing the
>> NFSROOT_TIMEOUT_MIN and NFSROOT_TIMEOUT_MAX values.
>>
>> Current strategy is, if do_mount_root fails, sleep for 5 seconds for the
>> second attempt followed by a 5<<1 seconds delay for each loop with a
>> maximum of 30 seconds delay.
>> For 5 retries it would take.
>>
>> 	5 + 10 + 20 + 30 + 30 = 95 Seconds
>> with
>> 	each do_mount_root timeout @ 3-4 seconds x 5 = 15 seconds.
>>
>> Which means Kernel can only attempt the succession root-mounts or panic
>> after 110 seconds.
>>
>> So changing min and max timeouts will have the below delays.
>> 	0  + 1 + 3 + 7 + 15	= 26 Seconds.
>> and with
>> 	each do_mount_root timeout @ 3-4 seconds x 5 = 15 seconds.
>> Which means Kernel can only attempt the succession root-mounts or panic
>> after 41 seconds
>>
>> As, do_mount_root timesout in 3-4 seconds which should be sufficient
>> delay to start of the second nfs mount attempt and increasing delay
>> after that makes more sense.
>>
>> I clearly see an advantange in changing these values because, Without
>> this patch my board mounts nfs in 9-10 seconds, however with this patch
>> can mount nfs in 4-5 seconds.
>>     
>
> This feels like tuning the default settings for a very specific set up.  In the original thread for this work, 41 seconds would probably not be long enough for the network switch to enable the port.
>   
Probably you might be right.
We could address that by increasing NFSROOT_RETRY_MAX to 7 from 5.

However, I want to highlight an another major issue of having an min
timeout start at 5.
Most of the boards (or SOC's) have in-build ethernet MAC's and external
Ethernet PHY's, Linux PHY (& phy state-machine) framework takes on an
average of 2-3 seconds from phy_start to get the ethernet PHY into a
Link-up state.
All those above boards which used to mount NFS in 3-4 seconds prior to
the original "NFS: Retry mounting NFSROOT" patch and few other patches,
NOW mounts NFS root in 9-10 seconds.
Which is the case with all the ST boards and most of the embedded boards
with external PHY's fall in.

Having the timeout start from 0 will address the uses case mentioned
above and increasing the loops from 5 to 8 will increase the total NFS
root timeout to 109 seconds.

0  + 1 + 3 + 7 + 15 + 31 + 31  = 88
 + 
each do_mount_root timeout @ 3-4 seconds x 7 = 21 = 109 seconds


Finally the intention of the patch was to address most of the use-cases
and not just the one I hit, increasing the retries to 7 should address
the orignal network switch case and reducing the timeout-min should help
other boards do nfs mounts as quickly as it used to happen before.

Let me know if this sounds OK to you so that I can generate a new patch?



Thanks,
srini
> I don't have a better solution at this time, but I think the current defaults will work (possibly with added delay) on most systems, whereas the proposed settings will probably result in more panics.  I prefer to keep the current settings until we have a solution that doesn't break other systems.
>
>   
>> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
>> ---
>> Hello All,
>> With latest kernel I can see that my nfs-root mounts with big delay
>> of 5 seconds when compared to 2.6.32. It took 9-10 seconds, where as in 2.6.32 it took 4-5 seconds.
>>
>> However with modifications to NFSROOT_TIMEOUT_MIN and NFSROOT_TIMEOUT_MAX,  nfs root mounts as it used to do it in 2.6.32.
>> As first nfs mount timeout itself introduces sufficient delay to start the second retry.
>> I think changing the min-max values will help people to nfs boot there boards faster than it is in 3.3 kernel.
>>
>> Comments ?
>>
>> Thanks.
>> srini
>>
>>
>>
>> init/do_mounts.c |    6 +++---
>> 1 files changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/init/do_mounts.c b/init/do_mounts.c
>> index ef6478f..b8214ce 100644
>> --- a/init/do_mounts.c
>> +++ b/init/do_mounts.c
>> @@ -361,8 +361,8 @@ out:
>>
>> #ifdef CONFIG_ROOT_NFS
>>
>> -#define NFSROOT_TIMEOUT_MIN	5
>> -#define NFSROOT_TIMEOUT_MAX	30
>> +#define NFSROOT_TIMEOUT_MIN	1
>> +#define NFSROOT_TIMEOUT_MAX	32
>> #define NFSROOT_RETRY_MAX	5
>>
>> static int __init mount_nfs_root(void)
>> @@ -390,7 +390,7 @@ static int __init mount_nfs_root(void)
>> 			break;
>>
>> 		/* Wait, in case the server refused us immediately */
>> -		ssleep(timeout);
>> +		ssleep(timeout - 1);
>> 		timeout <<= 1;
>> 		if (timeout > NFSROOT_TIMEOUT_MAX)
>> 			timeout = NFSROOT_TIMEOUT_MAX;
>> -- 
>> 1.6.3.3
>>
>> --
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>>     
>
>