Re: [PATCH] only irq-safe atomic ops

Stephen Lord
2002-02-23T20:00:23Z

Andrew Morton wrote:

>Robert Love wrote:
>
>>...
>>
>>Question: if (from below) you are going to use atomic operations, why
>>make it per-CPU at all? Just have one counter and atomic_inc and
>>atomic_read it. You won't need a spin lock.
>>
>
>Oh that works fine. But then it's a global counter, so each time
>a CPU marks a page dirty, the counter needs to be pulled out of
>another CPU's cache. Which is not a thing I *need* to do.
>
>As I said, it's a micro-issue. But it's a requirement which
>may pop up elsewhere.
>
>
I can tell you that Irix has just such a global counter for the amount of
delayed allocate pages - and it gets to be a major point of cache contention
once you get to larger cpu counts. So avoiding that from the start would
be good.

Steve