netdev - Re: [PATCH] netpoll: Drop budget parameter from NAPI polling call hierarchy

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Message-Id: <20150929.134846.1031290048722134936.davem@davemloft.net>
Date:	Tue, 29 Sep 2015 13:48:46 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	alexander.duyck@...il.com
Cc:	aduyck@...antis.com, netdev@...r.kernel.org
Subject: Re: [PATCH] netpoll: Drop budget parameter from NAPI polling call
 hierarchy

From: Alexander Duyck <alexander.duyck@...il.com>
Date: Sun, 27 Sep 2015 15:58:56 -0700

> On 09/26/2015 10:36 PM, David Miller wrote:
>> From: Alexander Duyck <aduyck@...antis.com>
>> Date: Tue, 22 Sep 2015 14:56:08 -0700
>>
>>> Rather than carry around a value of budget that is 0 or less we can
>>> instead
>>> just loop through and pass 0 to each napi->poll call.  If any driver
>>> returns a value for work done that is non-zero then we can report that
>>> driver and continue rather than allowing a bad actor to make the
>>> budget
>>> value negative and pass that negative value to napi->poll.
>> Unfortunately we have drivers that won't do any TX work if the budget
>> is zero.
> 
> Well that is what we are doing right now.  The fact is the call starts
> out with a budget of 0, and it is somewhat hidden from the call since
> the budget is assigned a value of 0 in netpoll_poll_dev. That is one
> of the things I was wanting do address because that is clear as mud
> from looking at poll_one_napi.  Based on the code you would assume
> budget starts out as a non-zero value and it doesn't.

I see, thanks for explaining.
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