Re: [RFC PATCH 0/6] Convert all tasklets to workqueues

[Duncan Sands <duncan.sands@math.u-psud.fr>]

Hi,

> > Just look at the tasklet_disable() logic.
> 
> Do not count this.
> 
> Done this way because nobody needed that thing, except for _one_ place
> in keyboard/console driver, which was very difficult to fix that time,
> when vt code was utterly messy and not smp safe at all.
> 
> start_bh_atomic() was successfully killed, but we had to preserve analogue
> of disable_bh() with the same semantics for some time.
> It is deliberately implemented in a way, which does not impact hot paths
> and is easy to remove.
> 
> It is sad that some usb drivers started to use this creepy and
> useless thing.

the usbatm USB driver uses it in the methods for opening and closing a new network
connection, and on device disconnect.  Yes, tasklet_disable could be eliminated by
adding a spinlock.  However this would mean taking the lock every time a packet is
received or transmitted.  As it is, typically open occurs once, when the computer
boots, and close and disconnect also occur once each, when the computer shuts down.
I felt that three calls to tasklet_disable were better than a gazillion calls to
spin_(un)lock.  Please feel free to educate me :)

Ciao,

Duncan.
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