Re: [GIT PULL tip/genirq] Please pull from lost-spurious-irq
From: Tejun Heo
Date: Mon Aug 02 2010 - 16:56:58 EST
On 08/02/2010 08:52 PM, Thomas Gleixner wrote:
>> Ooh, another reason is timer locality. If timers are shared per desc,
>> they have much higher chance of being on the same processor. Global
>> timers would be pretty bad in that respect.
> That's irrelevant. If you need to poll an interrupt, then it does not
> matter at all whether you bounce some cache lines or not.
> In fact we have two cases:
> 1) An interrupt needs to be polled all the time. That sucks whether
> the poll timer bounces a few cache lines or not.
> 2) Polling an irq for some time. Either it works again after a
> while, so your suckage is restricted to the poll period. If not
> see #1
Hmm... for spurious and watch the above are true and if it were the
above two it would definitely make more sense to use per-purpose
global timers. The problem is w/ expect tho. It's supposed to be
used with normal hot paths, so expect/unexpect operations better be
low overhead and local. I'll talk more about it in the other reply.
> And it's even less of an issue as the main users of this misfeature
> are laptops and desktop machines, where locality is not really that
> important. If an enterprise admin decides to ignore the fact that the
> hardware is flaky, then he does not care about the cache line bounces
These problems do happen on intel chipset machines and is something
which can be worked around with some effort. Eh, let's talk on the
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