netdev - Re: [PATCH net-next 2/2] net: exit busy loop when another process is runnable

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Message-ID: <1408716976.5604.18.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 22 Aug 2014 07:16:16 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>, davem@...emloft.net,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	mst@...hat.com, Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH net-next 2/2] net: exit busy loop when another process
 is runnable

On Fri, 2014-08-22 at 17:08 +0800, Jason Wang wrote:

> But this is just for current process. We want to determine whether or
> not it was worth to loop busily in current process by checking if
> there's any another runnable processes or callbacks. And what we need
> here is just a simple and lockless hint which can't be wrong but may be
> inaccurate to exit the busy loop. The net code does not depends on this
> hint to do scheduling or yielding.
> 
> How about just introducing a boolean helper like current_can_busy_loop()
> and return true in one of the following conditions:
> 
> - Current task is SCHED_FIFO
> - Current task is neither SCHED_FIFO nor SCHED_IDLE and no other
> runnable processes or pending RCU callbacks in current cpu
> 
> And add warns to make sure it can only be called in process context.


1) Any reasons Eliezer Tamir is not included in the CC list ?

   He is the busypoll author after all, and did nothing wrong to be
banned from these patches ;)

2) It looks like sk_buy_loop() should not be inlined, its is already too
big.




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