Subject: Re: SMP re-eetrancy in "bottom half" drivers
To: Warner Losh <firstname.lastname@example.org>
From: Jonathan Stone <email@example.com>
Date: 05/17/2005 13:25:09
In message <firstname.lastname@example.org>,
Warner Losh writes:
>> Yes; your old patch for i386 SMP effectively collapsed all SPLs to a
>> single level. That way, no driver should interrupt another.
>Make careful measurements as to how this impacts interrupt latency.
>Having the serial driver interrupt the audio driver to process
>characters is a good thing (16550's have a much lower latency
>tolerance than do most audio devices). If too much of the kernel
>blocks interrupts entirely, this can create starvation for things like
>16550 RX FIFOs.
That goes without saying. I've ben dealing with that since DZ-11s and
4856es with 16450s. Yamamoto-san's patch was for experimentation,
labelled: for someone interested to try).
The biggest --- perhaps the only -- unresolved technical issue from
last time this came up centered around locking and SPL issues. My
recollection is that there was a near-consensus that we'd need to move
to a total ordering of locks and SPLs; but I may well be misremembering.