Re: Stop using tasklets for bottom halves

[Luis R. Rodriguez]

On Mon, Sep 7, 2009 at 7:17 PM, Steven Rostedt<rostedt@xxxxxxxxxxx> 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@xxxxxxxxx> 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/
>> >
>> > Â Luis
>> > --
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>>
>> 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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