netdev - Re: [Intel-wired-lan] [PATCH iwl-net v3 2/6] igc: Lengthen the hardware retry time to prevent timeouts

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Message-ID: <4ee8f886-40ed-46bc-9d11-1619d64f7875@molgen.mpg.de>
Date: Thu, 7 Nov 2024 00:13:43 +0100
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Christopher S M Hall <christopher.s.hall@...el.com>
Cc: intel-wired-lan@...ts.osuosl.org, david.zage@...el.com,
 vinicius.gomes@...el.com, netdev@...r.kernel.org,
 rodrigo.cadore@...coustics.com, vinschen@...hat.com,
 Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>,
 Mor Bar-Gabay <morx.bar.gabay@...el.com>,
 Avigail Dahan <avigailx.dahan@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH iwl-net v3 2/6] igc: Lengthen the
 hardware retry time to prevent timeouts

Dear Christopher,


Thank you for the patch.

I’d use the more specific summary/title below:

igc: Lengthen hardware retry time to 4 μs to prevent timeouts

Am 06.11.24 um 19:47 schrieb Christopher S M Hall:
> Lengthen the hardware retry timer to four microseconds.
> 
> The i225/i226 hardware retries if it receives an inappropriate response
> from the upstream device. If the device retries too quickly, the root
> port does not respond.

Any idea why? Is it documented somewhere?

> The issue can be reproduced with the following:
> 
> $ sudo phc2sys -R 1000 -O 0 -i tsn0 -m
> 
> Note: 1000 Hz (-R 1000) is unrealistically large, but provides a way to
> quickly reproduce the issue.
> 
> PHC2SYS exits with:
> 
> "ioctl PTP_OFFSET_PRECISE: Connection timed out" when the PTM transaction
>    fails

Why four microseconds, and not some other value?

> Fixes: 6b8aa753a9f9 ("igc: Decrease PTM short interval from 10 us to 1 us")
> Reviewed-by: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
> Tested-by: Mor Bar-Gabay <morx.bar.gabay@...el.com>
> Tested-by: Avigail Dahan <avigailx.dahan@...el.com>
> Signed-off-by: Christopher S M Hall <christopher.s.hall@...el.com>
> ---
>   drivers/net/ethernet/intel/igc/igc_defines.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/intel/igc/igc_defines.h b/drivers/net/ethernet/intel/igc/igc_defines.h
> index 2ff292f5f63b..84521a4c35b4 100644
> --- a/drivers/net/ethernet/intel/igc/igc_defines.h
> +++ b/drivers/net/ethernet/intel/igc/igc_defines.h
> @@ -574,7 +574,7 @@
>   #define IGC_PTM_CTRL_SHRT_CYC(usec)	(((usec) & 0x3f) << 2)
>   #define IGC_PTM_CTRL_PTM_TO(usec)	(((usec) & 0xff) << 8)
>   
> -#define IGC_PTM_SHORT_CYC_DEFAULT	1   /* Default short cycle interval */
> +#define IGC_PTM_SHORT_CYC_DEFAULT	4   /* Default short cycle interval */
>   #define IGC_PTM_CYC_TIME_DEFAULT	5   /* Default PTM cycle time */
>   #define IGC_PTM_TIMEOUT_DEFAULT		255 /* Default timeout for PTM errors */


Kind regards,

Paul