netdev - Re: [PATCH net-next 2/5] ionic: smaller coalesce default

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Message-Id: <20200831.171613.1392501036623240615.davem@davemloft.net>
Date:   Mon, 31 Aug 2020 17:16:13 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     kuba@...nel.org
Cc:     snelson@...sando.io, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/5] ionic: smaller coalesce default

From: Jakub Kicinski <kuba@...nel.org>
Date: Mon, 31 Aug 2020 16:50:54 -0700

> On Mon, 31 Aug 2020 16:35:55 -0700 Shannon Nelson wrote:
>> diff --git a/drivers/net/ethernet/pensando/ionic/ionic_dev.h b/drivers/net/ethernet/pensando/ionic/ionic_dev.h
>> index 9e2ac2b8a082..2b2eb5f2a0e5 100644
>> --- a/drivers/net/ethernet/pensando/ionic/ionic_dev.h
>> +++ b/drivers/net/ethernet/pensando/ionic/ionic_dev.h
>> @@ -16,7 +16,7 @@
>>  #define IONIC_DEF_TXRX_DESC		4096
>>  #define IONIC_LIFS_MAX			1024
>>  #define IONIC_WATCHDOG_SECS		5
>> -#define IONIC_ITR_COAL_USEC_DEFAULT	64
>> +#define IONIC_ITR_COAL_USEC_DEFAULT	8
> 
> 8 us interrupt coalescing does not hurt general operations?! No way.
> 
> It's your customers who'll get hurt here, so your call, but I seriously
> doubt this. Unless the unit is not usec?

Agreed, 8usec is really really low.  You won't get much coalescing during
bulk transfers with a value like that, eliminating the gain from coalescing
in the first place.