linux-kernel - Re: Stop using tasklets for bottom halves

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Message-ID: <43e72e890909072116v33ecafc4ma7f5a68825f14e9@mail.gmail.com>
Date:	Mon, 7 Sep 2009 21:16:38 -0700
From:	"Luis R. Rodriguez" <mcgrof@...il.com>
To:	rostedt@...dmis.org
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	Ingo Molnar <mingo@...e.hu>, Michael Buesch <mb@...sch.de>,
	"John W. Linville" <linville@...driver.com>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Matt Smith <Matt.Smith@...eros.com>,
	Kevin Hayes <kevin@...eros.com>,
	Bob Copeland <me@...copeland.com>, Jouni Malinen <j@...fi>,
	Ivan Seskar <Seskar@...lab.rutgers.edu>, ic.felix@...il.com
Subject: Re: Stop using tasklets for bottom halves

On Mon, Sep 7, 2009 at 7:17 PM, Steven Rostedt<rostedt@...dmis.org> wrote:
> On Mon, 2009-09-07 at 17:14 -0700, Stephen Hemminger wrote:
>> On Mon, 7 Sep 2009 15:58:50 -0700
>> "Luis R. Rodriguez" <mcgrof@...il.com> wrote:
>>
>> > A while ago I had read about an effort to consider removing tasklets
>> > [1] or at least trying to not use them. I'm unaware of the progress in
>> > this respect but since reading that article have always tried to
>> > evaluate whether or not we need tasklets on wireless drivers. I have
>> > also wondered whether work in irq context in other parts of the kernel
>> > can be moved to process context, a curious example being timers. I'll
>> > personally be trying to using only process context on bottom halves on
>> > future drivers but I figured it may be a good time to ask how serious
>> > was avoiding tasklets or using wrappers in the future to avoid irq
>> > context is or is it advised. Do we have a general agreement this is a
>> > good step forward to take? Has anyone made tests or changes on a
>> > specific driver from irq context to process context and proven there
>> > are no significant advantages of using irq context where you would
>> > have expected it?
>> >
>> > Wireless in particular should IMHO not require taskets for anything
>> > time sensitive that I can think about except perhaps changing channels
>> > quickly and to do that appropriately also process pending RX frames
>> > prior to a switch. It remains to be seen experimentally whether or not
>> > using a workqueue for RX processing would affect the time to switch
>> > channels negatively but I doubt it would be significant. I hope to
>> > test that with ath9k_htc.
>> >
>> > What about gigabit or 10 Gigabit Ethernet drivers ? Do they face any
>> > challenges which would yet need to be proven would not face issues
>> > when processing bottom halves in process context?
>> >
>> > [1] http://lwn.net/Articles/239633/
>> >
>> >   Luis
>> > --
>> > To unsubscribe from this list: send the line "unsubscribe netdev" in
>> > the body of a message to majordomo@...r.kernel.org
>> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>> Why not use NAPI, which is soft irq? Almost all 1G and 10G drivers
>> use NAPI.
>>
>> Process context is too slow.
>
> Well, I'm hoping to prove the opposite. I'm working on some stuff that I
> plan to present at Linux Plumbers. I've been too distracted by other
> things, but hopefully I'll have some good numbers to present by then.

What day in specific was this planned for at Plumbers?

  Luis
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